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Practice › LeetCode › LeetCode 34xx ›

LeetCode 3430 - Maximum and Minimum Sums of at Most Size K Subarrays

LeetCode Problem 3430 Difficulty: 🔴 Hard Topics: Array, Math, Stack, Monotonic Stack Solution Problem Understanding We are remains efficient even at the maximum constraint limit.

Practice › LeetCode › LeetCode 38xx ›

LeetCode 3878 - Count Good Subarrays

LeetCode Problem 3878 Difficulty: 🔴 Hard Topics: Array, Stack, Bit Manipulation, Monotonic Stack Solution LeetCode 3878 - Count Good Subarrays Problem Understanding We are given an integer array nums , and we must count how many subarrays are good . A subarray is considered good if the bitwise OR of all elements in that subarray is equal to at least one element that appears inside the same subarray. Suppose a...

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LeetCode 3816 - Lexicographically Smallest String After Deleting Duplicate Characters

LeetCode Problem 3816 Difficulty: 🔴 Hard Topics: Hash Table, String, Stack, Greedy, Monotonic Stack Solution LeetCode 3816 - Lexicographically Smallest String After Deleting Duplicate Characters Problem Understanding We are given a string s consisting only of lowercase English letters. The allowed operation is very specific: if a character currently appears at least twice in the string, we may delete exactly one occurrence of that character. We may repeat this operation...

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LeetCode 3555 - Smallest Subarray to Sort in Every Sliding Window

LeetCode Problem 3555 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Stack, Greedy, Sorting, Monotonic Stack Solution Problem Understanding The problem asks us to examine every contiguous subarray (window) of length k in the array nums and determine the minimum continuous segment within that window that must be sorted to make the entire window non-decreasing. In other words, for each sliding window, we want the smallest subarray that, if sorted, results...

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LeetCode 3676 - Count Bowl Subarrays

LeetCode Problem 3676 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem asks us to count how many subarrays in an array of distinct integers satisfy a specific “bowl” condition. A subarray nums[l...r] is considered a bowl if it has length at least 3 and the smaller of its two endpoints is strictly greater than the maximum value of all elements strictly inside the subarray. In...

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LeetCode 3638 - Maximum Balanced Shipments

LeetCode Problem 3638 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Stack, Greedy, Monotonic Stack Solution Problem Understanding We are given an array weight representing parcels arranged in a line. We must partition some prefix-suffix segments of this array into a collection of non-overlapping contiguous subarrays called shipments. Each parcel can belong to at most one shipment, and it is also allowed to leave some parcels unused. A shipment is considered...

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LeetCode 3542 - Minimum Operations to Convert All Elements to Zero

LeetCode Problem 3542 Difficulty: 🟡 Medium Topics: Array, Hash Table, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem requires us to reduce all elements of a given non-negative integer array nums to zero using the fewest number of operations. Each operation allows selecting a contiguous subarray and setting all occurrences of the minimum non-negative integer in that subarray to zero. In essence, we can remove the "smallest" numbers in...

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LeetCode 3523 - Make Array Non-decreasing

LeetCode Problem 3523 Difficulty: 🟡 Medium Topics: Array, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem asks us to transform an integer array nums into a non-decreasing array by performing zero or more operations, where an operation consists of selecting a contiguous subarray and replacing it with its maximum value . The goal is to maximize the size of the resulting array after all operations. In other words, we...

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LeetCode 3420 - Count Non-Decreasing Subarrays After K Operations

LeetCode Problem 3420 Difficulty: 🔴 Hard Topics: Array, Stack, Segment Tree, Queue, Sliding Window, Monotonic Stack, Monotonic Queue Solution Problem Understanding You are given an array nums and a budget of at most k increment operations. For any chosen subarray, you may repeatedly pick an element inside that subarray and increase it by 1 . The goal is to determine whether that subarray can be transformed into a non-decreasing array...

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LeetCode 2487 - Remove Nodes From Linked List

LeetCode Problem 2487 Difficulty: 🟡 Medium Topics: Linked List, Stack, Recursion, Monotonic Stack Solution Problem Understanding The problem gives us the head of a singly linked list and asks us to remove every node that has a strictly greater value somewhere to its right. In other words, for each node, we must determine whether there exists another node later in the list whose value is larger. If such a node...

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LeetCode 3205 - Maximum Array Hopping Score I

LeetCode Problem 3205 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem asks us to calculate the maximum score achievable by hopping through an array from the first element to the last. You start at index 0 , and at each step, you can jump to any subsequent index j > i . When you jump, you accumulate a score of (j -...

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LeetCode 3221 - Maximum Array Hopping Score II

LeetCode Problem 3221 Difficulty: 🟡 Medium Topics: Array, Stack, Greedy, Monotonic Stack Solution LeetCode 3221 - Maximum Array Hopping Score II Problem Understanding The problem gives us an integer array nums , where each position represents a possible location we can stand on. We always begin at index 0 , and we must eventually reach the last index of the array. From any index i , we are allowed to...

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LeetCode 1856 - Maximum Subarray Min-Product

LeetCode Problem 1856 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack, Prefix Sum Solution Problem Understanding The problem asks us to find the maximum min-product of any contiguous subarray of a given integer array nums . The min-product of a subarray is defined as the minimum value in that subarray multiplied by the sum of all elements in that subarray . We are asked to return this maximum value modulo...

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LeetCode 3229 - Minimum Operations to Make Array Equal to Target

LeetCode Problem 3229 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem gives us two arrays, nums and target , both of the same length. We are allowed to perform operations on nums until it becomes exactly equal to target . In one operation, we choose any contiguous subarray and either: Increment every element in that subarray by 1 Decrement every element in...

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LeetCode 2866 - Beautiful Towers II

LeetCode Problem 2866 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem asks us to build a series of towers along a coordinate line, where each tower has a height constrained by a given maxHeights array. The resulting configuration must form a mountain array , meaning there is a single peak somewhere in the array, with tower heights non-decreasing up to the peak and non-increasing after...

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LeetCode 1996 - The Number of Weak Characters in the Game

LeetCode Problem 1996 Difficulty: 🟡 Medium Topics: Array, Stack, Greedy, Sorting, Monotonic Stack Solution Problem Understanding In this problem, every character in the game has two attributes: attack defense The input is a 2D array called properties , where: properties[i] = [attacki, defensei] represents the stats of the i-th character. A character is considered weak if there exists another character with: strictly greater attack strictly greater defense Both conditions must...

Practice › LeetCode › LeetCode 26xx ›

LeetCode 2617 - Minimum Number of Visited Cells in a Grid

LeetCode Problem 2617 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Stack, Breadth-First Search, Union-Find, Heap (Priority Queue), Matrix, Monotonic Stack Solution Problem Understanding The problem asks us to determine the minimum number of cells we need to visit in order to reach the bottom-right corner of a given m x n grid. Each cell (i, j) contains a number grid[i][j] representing the maximum number of steps we can move right...

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LeetCode 2818 - Apply Operations to Maximize Score

LeetCode Problem 2818 Difficulty: 🔴 Hard Topics: Array, Math, Stack, Greedy, Sorting, Monotonic Stack, Number Theory Solution Problem Understanding The problem gives us an array nums and an integer k . We begin with a score of 1 , and we are allowed to perform at most k operations. In each operation, we choose a subarray that has not been chosen before. From that subarray, we select the element with...

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LeetCode 2104 - Sum of Subarray Ranges

LeetCode Problem 2104 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution LeetCode 2104 - Sum of Subarray Ranges Problem Understanding The problem gives us an integer array nums , and asks us to compute the sum of the ranges of every possible non-empty contiguous subarray. The range of a subarray is defined as: maximum element - minimum element For every possible subarray, we calculate its range, then add all...

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LeetCode 2030 - Smallest K-Length Subsequence With Occurrences of a Letter

LeetCode Problem 2030 Difficulty: 🔴 Hard Topics: String, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem asks us to construct the lexicographically smallest subsequence of length k from the string s , while ensuring that a specific character, letter , appears at least repetition times in the resulting subsequence. A subsequence preserves the relative order of characters from the original string, but characters may be skipped. For example, from...

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LeetCode 1950 - Maximum of Minimum Values in All Subarrays

LeetCode Problem 1950 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution Problem Understanding This problem asks us to compute, for every possible subarray size, the best possible minimum value among all subarrays of that size. Given an array nums of length n , we must evaluate every window size from 1 to n . For each size k , we consider all contiguous subarrays of length k . Every...

Practice › LeetCode › LeetCode 33xx ›

LeetCode 3359 - Find Sorted Submatrices With Maximum Element at Most K

LeetCode Problem 3359 Difficulty: 🔴 Hard Topics: Array, Stack, Matrix, Monotonic Stack Solution Problem Understanding We are given a matrix grid with m rows and n columns, along with an integer k . The task is to count how many rectangular submatrices satisfy two conditions simultaneously: Every value inside the submatrix must be at most k . Every row inside the submatrix must be sorted in non-increasing order from left...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2736 - Maximum Sum Queries

LeetCode Problem 2736 Difficulty: 🔴 Hard Topics: Array, Binary Search, Stack, Binary Indexed Tree, Segment Tree, Sorting, Monotonic Stack Solution LeetCode 2736 - Maximum Sum Queries Problem Understanding We are given two arrays, nums1 and nums2 , both of length n . Each index j represents a point: $$(nums1[j], nums2[j])$$ and has an associated value: $$nums1[j] + nums2[j]$$ For every query [xi, yi] , we must find an index j...

Practice › LeetCode › LeetCode 22xx ›

LeetCode 2297 - Jump Game VIII

LeetCode Problem 2297 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Stack, Graph Theory, Monotonic Stack, Shortest Path Solution Problem Understanding This problem asks us to compute the minimum total cost required to move from index 0 to index n - 1 in an array. The movement rules are unusual because whether a jump is valid depends not only on the values at the start and destination indices, but also on...

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LeetCode 2289 - Steps to Make Array Non-decreasing

LeetCode Problem 2289 Difficulty: 🟡 Medium Topics: Array, Linked List, Dynamic Programming, Stack, Monotonic Stack, Simulation Solution Problem Understanding The problem asks us to determine how many steps it takes to make a given array nums non-decreasing by repeatedly removing elements that break the non-decreasing property. Specifically, for each step, any element nums[i] where nums[i - 1] > nums[i] is removed. This process continues until the array is entirely non-decreasing....

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LeetCode 2355 - Maximum Number of Books You Can Take

LeetCode Problem 2355 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Stack, Monotonic Stack Solution That is a long, multi-section technical reference document. I can provide the full guide, but it will be quite extensive. Before I start, do you want the complete solution guide for LeetCode 2355 - Maximum Number of Books You Can Take in one single response , including all required sections (Problem Understanding, Approaches, Algorithm Walkthrough, Python...

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LeetCode 2281 - Sum of Total Strength of Wizards

LeetCode Problem 2281 Difficulty: 🔴 Hard Topics: Array, Stack, Monotonic Stack, Prefix Sum Solution Problem Understanding The problem asks us to compute the sum of total strengths across every possible contiguous subarray of the input array strength . For any chosen subarray, its total strength is defined as: $$\text{minimum value in subarray} \times \text{sum of values in subarray}$$ We must evaluate this quantity for all non-empty contiguous subarrays , then...

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LeetCode 2282 - Number of People That Can Be Seen in a Grid

LeetCode Problem 2282 Difficulty: 🟡 Medium Topics: Array, Stack, Matrix, Monotonic Stack Solution Problem Understanding The problem asks us to determine, for each person in a 2D grid of heights, how many other people they can see according to a specific line-of-sight rule. Each person at position (i, j) can see another person either directly to the right in the same row or directly below in the same column. The...

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LeetCode 2940 - Find Building Where Alice and Bob Can Meet

LeetCode Problem 2940 Difficulty: 🔴 Hard Topics: Array, Binary Search, Stack, Binary Indexed Tree, Segment Tree, Heap (Priority Queue), Monotonic Stack Solution Problem Understanding You are given an array heights , where each index represents a building and the value represents that building's height. A person standing at building i can move only to the right, meaning to some building j where j > i , and only if the...

Practice › LeetCode › LeetCode 28xx ›

LeetCode 2865 - Beautiful Towers I

LeetCode Problem 2865 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem asks us to transform an array of tower heights into a mountain-shaped arrangement while removing as few bricks as necessary. A mountain-shaped arrangement is defined as one where tower heights first non-decrease up to a peak (or consecutive peaks of the same height) and then non-increase after the peak. We are not allowed to...

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LeetCode 2832 - Maximal Range That Each Element Is Maximum in It

LeetCode Problem 2832 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution LeetCode 2832 - Maximal Range That Each Element Is Maximum in It Problem Understanding We are given an array nums consisting of distinct integers. For every position i , we need to determine the maximum possible length of a contiguous subarray in which nums[i] is the largest element. More formally, for each index i , we want to...

Practice › LeetCode › LeetCode 23xx ›

LeetCode 2345 - Finding the Number of Visible Mountains

LeetCode Problem 2345 Difficulty: 🟡 Medium Topics: Array, Stack, Sorting, Monotonic Stack Solution LeetCode 2345 - Finding the Number of Visible Mountains Problem Understanding Each mountain is represented by a peak point (x, y) . Because the mountain is a right-angled isosceles triangle with slopes +1 and -1 , its shape is completely determined by its peak. For a mountain with peak (x, y) : The left boundary touches the...

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LeetCode 3113 - Find the Number of Subarrays Where Boundary Elements Are Maximum

LeetCode Problem 3113 Difficulty: 🔴 Hard Topics: Array, Binary Search, Stack, Monotonic Stack Solution Problem Understanding We are given an array nums of positive integers. We need to count how many contiguous subarrays satisfy a very specific condition: The first element of the subarray and the last element of the subarray must both be equal to the maximum value inside that subarray. In other words, for a subarray nums[l:r+1] ,...

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LeetCode 1944 - Number of Visible People in a Queue

LeetCode Problem 1944 Difficulty: 🔴 Hard Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem gives a queue of n people standing from left to right, where each person has a distinct height. For each person i , we need to determine how many people to their right they can see. A person i can see a person j (with j > i ) if every person between them...

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LeetCode 2334 - Subarray With Elements Greater Than Varying Threshold

LeetCode Problem 2334 Difficulty: 🔴 Hard Topics: Array, Stack, Union-Find, Monotonic Stack Solution Problem Understanding This problem asks us to find a contiguous subarray whose elements are all sufficiently large relative to the subarray length. More specifically, for a subarray of length k , every element inside that subarray must satisfy: $$\text{element} > \frac{\text{threshold}}{k}$$ We are allowed to return the size k of any valid subarray. If no such subarray...

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LeetCode 2863 - Maximum Length of Semi-Decreasing Subarrays

LeetCode Problem 2863 Difficulty: 🟡 Medium Topics: Array, Stack, Sorting, Monotonic Stack Solution LeetCode 2863 - Maximum Length of Semi-Decreasing Subarrays Problem Understanding The problem gives us an integer array nums and asks for the length of the longest contiguous subarray whose first element is strictly greater than its last element. A subarray is any contiguous segment of the array. For a subarray nums[i...j] to be considered semi-decreasing, the following...

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LeetCode 1966 - Binary Searchable Numbers in an Unsorted Array

LeetCode Problem 1966 Difficulty: 🟡 Medium Topics: Array, Binary Search, Stack, Monotonic Stack Solution Problem Understanding This problem asks us to identify how many numbers in an unsorted array are still guaranteed to be found by a randomized binary-search-like process. The array nums contains unique integers. The search procedure repeatedly chooses a random pivot element from the current remaining sequence. Depending on whether the pivot is smaller or larger than...

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LeetCode 2454 - Next Greater Element IV

LeetCode Problem 2454 Difficulty: 🔴 Hard Topics: Array, Binary Search, Stack, Sorting, Heap (Priority Queue), Monotonic Stack Solution Problem Understanding The problem asks us to compute, for every element in the array, its "second greater element" to the right. For an index i , we are interested in elements positioned after i . Among those elements, we only care about values strictly greater than nums[i] . The second greater element...

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LeetCode 2945 - Find Maximum Non-decreasing Array Length

LeetCode Problem 2945 Difficulty: 🔴 Hard Topics: Array, Binary Search, Dynamic Programming, Stack, Queue, Monotonic Stack, Monotonic Queue Solution Problem Understanding This problem asks us to determine the maximum length of a non-decreasing array that can be obtained from a given integer array nums by performing a sequence of subarray sum operations . In each operation, we can choose any contiguous subarray, replace it with a single element equal to...

Practice › LeetCode › LeetCode 09xx ›

LeetCode 901 - Online Stock Span

LeetCode Problem 901 Difficulty: 🟡 Medium Topics: Stack, Design, Monotonic Stack, Data Stream Solution Problem Understanding The problem asks us to design a class that processes stock prices one day at a time and, for every new price, returns the stock span for that day. The stock span is defined as the number of consecutive days ending today where the stock price was less than or equal to today's price....

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LeetCode 1475 - Final Prices With a Special Discount in a Shop

LeetCode Problem 1475 Difficulty: 🟢 Easy Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem presents a scenario where you are buying items in a shop, each with a given price stored in an array prices . For each item at index i , there may exist a discount based on the next item j (where j > i ) such that prices[j] <= prices[i] . If such a...

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LeetCode 84 - Largest Rectangle in Histogram

LeetCode Problem 84 Difficulty: 🔴 Hard Topics: Array, Stack, Monotonic Stack Solution LeetCode 84 - Largest Rectangle in Histogram Problem Understanding This problem asks us to find the largest rectangular area that can be formed inside a histogram. A histogram is represented as an array of integers called heights , where each integer describes the height of a bar, and every bar has a width of exactly 1 . The...

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LeetCode 1526 - Minimum Number of Increments on Subarrays to Form a Target Array

LeetCode Problem 1526 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem gives us a target array and asks us to build it starting from an array of all zeros. The only operation allowed is selecting any contiguous subarray and incrementing every element in that subarray by exactly one. The goal is to determine the minimum number of such operations required to transform...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 739 - Daily Temperatures

LeetCode Problem 739 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem gives an array called temperatures , where each element represents the temperature recorded on a specific day. For every day, we must determine how many days in the future we need to wait until a warmer temperature appears. If there is no future day with a higher temperature, the answer for that position should...

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LeetCode 456 - 132 Pattern

LeetCode Problem 456 Difficulty: 🟡 Medium Topics: Array, Binary Search, Stack, Monotonic Stack, Ordered Set Solution Problem Understanding The problem asks us to determine whether an array contains a specific ordering pattern called a "132 pattern". A valid 132 pattern consists of three indices i , j , and k such that: i < j < k nums[i] < nums[k] < nums[j] The name "132" comes from the relative ordering...

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LeetCode 1574 - Shortest Subarray to be Removed to Make Array Sorted

LeetCode Problem 1574 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Binary Search, Stack, Monotonic Stack Solution Please provide the full problem statement or LeetCode number you want the detailed solution guide for. You mentioned LeetCode 1574 - Shortest Subarray to be Removed to Make Array Sorted , so I can generate the complete guide with all requested sections: Problem Understanding Approaches (Brute Force + Optimal) Comparison Table Algorithm Walkthrough Python...

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LeetCode 1762 - Buildings With an Ocean View

LeetCode Problem 1762 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution LeetCode 1762, Buildings With an Ocean View Problem Understanding This problem gives us an array called heights , where each element represents the height of a building. The buildings are arranged in a straight line from left to right, and the ocean is located to the right side of the last building. A building has an ocean view...

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LeetCode 316 - Remove Duplicate Letters

LeetCode Problem 316 Difficulty: 🟡 Medium Topics: String, Stack, Greedy, Monotonic Stack Solution LeetCode 316, Remove Duplicate Letters Problem Understanding This problem asks us to construct a new string from the input string s such that every distinct character appears exactly once, while also ensuring that the final result is the smallest possible in lexicographical order. The input is a string consisting only of lowercase English letters. Characters may appear...

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LeetCode 1776 - Car Fleet II

LeetCode Problem 1776 Difficulty: 🔴 Hard Topics: Array, Math, Stack, Heap (Priority Queue), Monotonic Stack Solution Problem Understanding The problem is asking us to compute the time at which each car in a line of cars collides with the car immediately in front of it, or return -1 if it never collides. Each car is represented by its position and speed. The cars are initially sorted by position in increasing...

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LeetCode 1081 - Smallest Subsequence of Distinct Characters

LeetCode Problem 1081 Difficulty: 🟡 Medium Topics: String, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem asks us to construct the lexicographically smallest subsequence of a string that contains every distinct character exactly once. A subsequence is formed by deleting zero or more characters without changing the relative order of the remaining characters. This is important because we are not allowed to rearrange characters arbitrarily. The final answer must...

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LeetCode 1019 - Next Greater Node In Linked List

LeetCode Problem 1019 Difficulty: 🟡 Medium Topics: Array, Linked List, Stack, Monotonic Stack Solution Problem Understanding The problem asks us to process a singly-linked list and, for each node, determine the value of the next node that has a strictly larger value. Concretely, if the list is [2,1,5] , for the first node 2 , the next larger node is 5 ; for the second node 1 , the next...

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LeetCode 853 - Car Fleet

LeetCode Problem 853 Difficulty: 🟡 Medium Topics: Array, Stack, Sorting, Monotonic Stack Solution Problem Understanding The problem describes a set of cars driving toward the same destination, represented by the integer target . Each car starts at a unique position and moves at a constant speed. Cars cannot overtake each other. If a faster car catches up to a slower car ahead of it, the faster car must slow down...

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LeetCode 975 - Odd Even Jump

LeetCode Problem 975 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Stack, Sorting, Monotonic Stack, Ordered Set Solution Problem Understanding The problem asks us to determine how many starting indices in an array allow reaching the last element by performing a series of jumps defined as either odd-numbered or even-numbered. The distinction between odd and even jumps is crucial: odd-numbered jumps must move to the smallest value greater than or equal...

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LeetCode 1504 - Count Submatrices With All Ones

LeetCode Problem 1504 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Stack, Matrix, Monotonic Stack Solution Problem Understanding The problem gives us an m x n binary matrix where each cell contains either 0 or 1 . We must count how many rectangular submatrices consist entirely of ones. A submatrix is any contiguous rectangular region inside the matrix. For every possible rectangle, we need to determine whether every element inside it...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 769 - Max Chunks To Make Sorted

LeetCode Problem 769 Difficulty: 🟡 Medium Topics: Array, Stack, Greedy, Sorting, Monotonic Stack Solution Problem Understanding This problem is asking us to determine the maximum number of contiguous chunks into which we can split an array such that sorting each chunk individually and concatenating them results in a fully sorted array. The input array arr is a permutation of integers from 0 to n-1 , meaning it contains each integer...

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LeetCode 1130 - Minimum Cost Tree From Leaf Values

LeetCode Problem 1130 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem asks us to construct a binary tree from an input array arr of positive integers, where each integer represents a leaf node in an in-order traversal. Every non-leaf node has exactly two children, and its value is calculated as the product of the largest leaf values in its left and right...

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LeetCode 321 - Create Maximum Number

LeetCode Problem 321 Difficulty: 🔴 Hard Topics: Array, Two Pointers, Stack, Greedy, Monotonic Stack Solution LeetCode 321 - Create Maximum Number Problem Understanding This problem asks us to build the lexicographically largest possible number of length k using digits taken from two arrays, nums1 and nums2 . Each array represents a sequence of digits from a number. We are allowed to choose some digits from nums1 and some digits from...

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LeetCode 1793 - Maximum Score of a Good Subarray

LeetCode Problem 1793 Difficulty: 🔴 Hard Topics: Array, Two Pointers, Binary Search, Stack, Monotonic Stack Solution Problem Understanding In this problem, we are given an integer array nums and a specific index k . We must find a contiguous subarray that contains index k , and among all such subarrays, maximize the following score: $$\text{score} = \min(\text{subarray}) \times \text{length of subarray}$$ The minimum element inside the chosen subarray determines the...

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LeetCode 1124 - Longest Well-Performing Interval

LeetCode Problem 1124 Difficulty: 🟡 Medium Topics: Array, Hash Table, Stack, Monotonic Stack, Prefix Sum Solution Edit LeetCode 1124 - Longest Well-Performing Interval Problem Understanding The problem gives us an array hours , where each element represents the number of hours an employee worked on a specific day. A day is classified as tiring if the employee worked strictly more than 8 hours . Otherwise, the day is considered non-tiring...

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LeetCode 255 - Verify Preorder Sequence in Binary Search Tree

LeetCode Problem 255 Difficulty: 🟡 Medium Topics: Array, Stack, Tree, Binary Search Tree, Recursion, Monotonic Stack, Binary Tree Solution Problem Understanding The problem gives an array of unique integers called preorder . This array is supposed to represent the preorder traversal of a binary search tree, and we must determine whether such a BST could actually exist. In a preorder traversal, nodes are visited in this order: Visit the current...

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LeetCode 42 - Trapping Rain Water

LeetCode Problem 42 Difficulty: 🔴 Hard Topics: Array, Two Pointers, Dynamic Programming, Stack, Monotonic Stack Solution Problem Understanding The problem gives an array called height , where each element represents the height of a vertical bar in an elevation map. Every bar has width 1 . After rainfall, water may become trapped between taller bars. The task is to compute the total amount of water that can be trapped. For...

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LeetCode 907 - Sum of Subarray Minimums

LeetCode Problem 907 Difficulty: 🟡 Medium Topics: Array, Dynamic Programming, Stack, Monotonic Stack Solution Problem Understanding The problem asks us to compute the sum of the minimum value of every possible contiguous subarray of a given array. For an array arr , every contiguous slice of the array is considered a subarray. For each subarray, we determine its minimum element. The final answer is the sum of all of those...

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LeetCode 1063 - Number of Valid Subarrays

LeetCode Problem 1063 Difficulty: 🔴 Hard Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem is asking us to count the number of valid subarrays in a given integer array nums . A subarray is valid if its leftmost element is not larger than any other element in the subarray. In other words, for a subarray starting at index i and ending at index j , the condition nums[i]...

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LeetCode 581 - Shortest Unsorted Continuous Subarray

LeetCode Problem 581 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Stack, Greedy, Sorting, Monotonic Stack Solution Problem Understanding The problem gives an integer array nums and asks for the length of the shortest continuous subarray such that, if only that subarray is sorted in non-decreasing order, the entire array becomes sorted. In other words, the array is "almost sorted", except for some misplaced elements. We need to identify the smallest...

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LeetCode 1008 - Construct Binary Search Tree from Preorder Traversal

LeetCode Problem 1008 Difficulty: 🟡 Medium Topics: Array, Stack, Tree, Binary Search Tree, Monotonic Stack, Binary Tree Solution Let's dive deep and construct a thorough technical guide for LeetCode 1008, following your formatting rules. Problem Understanding The problem asks us to construct a binary search tree (BST) from a given preorder traversal array. A preorder traversal is defined as visiting the root node first, then recursively visiting the left subtree,...

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LeetCode 85 - Maximal Rectangle

LeetCode Problem 85 Difficulty: 🔴 Hard Topics: Array, Dynamic Programming, Stack, Matrix, Monotonic Stack Solution Problem Understanding The problem asks us to find the area of the largest rectangle containing only 1 s in a binary matrix. The matrix consists of characters '0' and '1' , where '1' represents a valid cell that may belong to a rectangle and '0' represents a blocked cell that cannot be included. The key...

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LeetCode 503 - Next Greater Element II

LeetCode Problem 503 Difficulty: 🟡 Medium Topics: Array, Stack, Monotonic Stack Solution Problem Understanding The problem gives us a circular array nums , and for every element, we must find the next greater element . The phrase next greater element means the first value encountered while moving forward in the array that is strictly larger than the current number. The key complication is that the array is circular . Normally,...

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LeetCode 496 - Next Greater Element I

LeetCode Problem 496 Difficulty: 🟢 Easy Topics: Array, Hash Table, Stack, Monotonic Stack Solution Problem Understanding The problem is asking us to find the next greater element for each element in nums1 within another array nums2 . Formally, for each element in nums1 , we need to locate its position in nums2 and then find the first element to its right in nums2 that is greater than itself . If...

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LeetCode 402 - Remove K Digits

LeetCode Problem 402 Difficulty: 🟡 Medium Topics: String, Stack, Greedy, Monotonic Stack Solution Problem Understanding The problem gives us a numeric string num and an integer k . We must remove exactly k digits from the number so that the resulting integer is as small as possible. The key detail is that we are not allowed to reorder digits. We may only delete digits while preserving the relative order of...

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LeetCode 768 - Max Chunks To Make Sorted II

LeetCode Problem 768 Difficulty: 🔴 Hard Topics: Array, Stack, Greedy, Sorting, Monotonic Stack Solution Problem Understanding The problem asks us to partition an array into the maximum possible number of contiguous chunks such that, after sorting each chunk independently and concatenating the results, the entire array becomes globally sorted. The key detail is that each chunk must remain contiguous. We cannot rearrange elements across chunk boundaries after splitting. Once the...

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LeetCode 962 - Maximum Width Ramp

LeetCode Problem 962 Difficulty: 🟡 Medium Topics: Array, Two Pointers, Stack, Monotonic Stack Solution Problem Understanding The problem asks us to find the maximum width ramp in an array of integers. A ramp is defined as a pair of indices (i, j) such that: i < j nums[i] <= nums[j] The width of the ramp is simply the distance between the two indices: $$\text{width} = j - i$$ Our goal...

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LeetCode 1673 - Find the Most Competitive Subsequence

LeetCode Problem 1673 Difficulty: 🟡 Medium Topics: Array, Stack, Greedy, Monotonic Stack Solution Here is a complete, detailed technical solution guide for LeetCode 1673 - Find the Most Competitive Subsequence following your formatting rules. Problem Understanding The problem asks us to find the most competitive subsequence of a given integer array nums of size k . A subsequence is formed by deleting zero or more elements from the array without...

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LeetCode 654 - Maximum Binary Tree

LeetCode Problem 654 Difficulty: 🟡 Medium Topics: Array, Divide and Conquer, Stack, Tree, Monotonic Stack, Binary Tree Solution Problem Understanding The problem asks us to construct a maximum binary tree from a given integer array nums with unique elements. A maximum binary tree is a binary tree where each node is the maximum element of the subarray it represents. Specifically, the root of the tree is the largest element in...

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LeetCode 1019: Next Greater Node In Linked List

Problem Restatement We are given the head of a singly linked list. For each node, we want to find the value of the next node that has a strictly greater value. If no such node exists, the answer for that node is 0 . Return an array of these answers. The official constraints state that the number of nodes is in [1, 10^4] and 1 <= Node.val <= 10^9 ....

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LeetCode 1063: Number of Valid Subarrays

Problem Restatement We are given an integer array nums . A valid subarray is one where nums[left] <= nums[i] for all left <= i <= right . In other words, the minimum of the subarray is at the leftmost position. Return the number of valid subarrays. The official constraints state that 1 <= nums.length <= 50000 . Input and Output Item Meaning Input Array nums Output Number of subarrays where...

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LeetCode 1081: Smallest Subsequence of Distinct Characters

Problem Restatement We are given a string s . We need to return the lexicographically smallest subsequence of s that contains all distinct characters of s exactly once. The official constraints state that 1 <= s.length <= 1000 and s consists of lowercase English letters. Note: This problem is identical to LeetCode 316 (Remove Duplicate Letters). Input and Output Item Meaning Input String s Output Lexicographically smallest subsequence with each...

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LeetCode 975: Odd Even Jump

Problem Restatement We are given an integer array arr . From any starting index, we make jumps to the right. The jumps are numbered by jump count: Jump number Type 1st , 3rd , 5th , ... Odd jump 2nd , 4th , 6th , ... Even jump For an odd jump from index i , we must jump to an index j such that: i < j arr[i] <=...

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LeetCode 768: Max Chunks To Make Sorted II

Problem Restatement We are given an integer array arr . We want to split it into some number of chunks. Then we sort each chunk individually and concatenate the sorted chunks back in the same order. The final result must equal the fully sorted version of arr . Return the maximum number of chunks we can make. The array may contain duplicate values. Input and Output Item Meaning Input An...

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LeetCode 962: Maximum Width Ramp

Problem Restatement We are given an integer array nums . A ramp is a pair of indices (i, j) such that: i < j nums[i] <= nums[j] The width of the ramp is: j - i Return the maximum possible width of a ramp. If no valid ramp exists, return 0 . The official constraints are: Constraint Value nums.length 2 <= nums.length <= 5 * 10^4 nums[i] 0 <= nums[i]...

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LeetCode 739: Daily Temperatures

Problem Restatement We are given an array temperatures . Each value represents the temperature on one day. For every day i , we need to find how many days we must wait until a future day has a strictly warmer temperature. If no warmer future day exists, the answer for that day is 0 . The official problem asks for an array answer where answer[i] is the number of days...

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LeetCode 907: Sum of Subarray Minimums

Problem Restatement We are given an integer array arr . For every contiguous subarray, take the minimum value of that subarray. Return the sum of all those minimum values. Because the answer can be large, return it modulo: 10**9 + 7 For example: arr = [3, 1, 2, 4] All subarray minimums are: [3] -> 3 [3, 1] -> 1 [3, 1, 2] -> 1 [3, 1, 2, 4] ->...

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LeetCode 654: Maximum Binary Tree

Problem Restatement We are given an array of distinct integers called nums . We must construct a binary tree using the following rules: The root is the maximum number in the array. The left subtree is built recursively from the elements to the left of the maximum number. The right subtree is built recursively from the elements to the right of the maximum number. Return the root of the constructed...

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LeetCode 503: Next Greater Element II

Problem Restatement We are given a circular integer array nums . For each element, we need to find the next greater element after it. The word circular means that after the last element, we continue again from the first element. If no greater element exists, the answer for that position is -1 . The official problem asks us to return the next greater number for every element in a circular...

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LeetCode 901: Online Stock Span

Problem Restatement We need to design a class called StockSpanner . The class receives stock prices one day at a time through the method next(price) . For each new price, we return its stock span. The span is the number of consecutive days ending today where each price was less than or equal to today's price. For example: prices = [100, 80, 60, 70, 60, 75, 85] The spans are:...

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LeetCode 496: Next Greater Element I

Problem Restatement We are given two arrays: Array Meaning nums1 Query numbers nums2 A larger reference array Every value in both arrays is unique, and every value in nums1 appears in nums2 . For each value x in nums1 , we need to find the first greater number appearing to the right of x inside nums2 . If no greater value exists, return -1 for that number. Input and Output...

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LeetCode 321: Create Maximum Number

Problem Restatement We are given two arrays of digits: nums1 nums2 They represent two numbers. We are also given an integer k . We need to create the maximum possible number of length k by taking digits from the two arrays. Rules: We may take digits from both arrays. We must take exactly k digits total. The relative order of digits taken from the same array must be preserved. Return...

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LeetCode 316: Remove Duplicate Letters

Problem Restatement We are given a string s containing lowercase English letters. We need to remove duplicate letters so that every distinct letter appears exactly once. Among all valid results, return the lexicographically smallest one. The official constraints are: Constraint Value s.length 1 <= s.length <= 10^4 Characters Lowercase English letters This problem is also the same as LeetCode 1081, Smallest Subsequence of Distinct Characters. ( github.com ) Input and...

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LeetCode 85: Maximal Rectangle

Problem Restatement We are given a binary matrix filled with characters: "0" "1" We need to find the largest rectangle that contains only "1" cells and return its area. The rectangle must be axis-aligned. That means its sides follow the matrix rows and columns. The official problem states: given a rows x cols binary matrix filled with 0 s and 1 s, find the largest rectangle containing only 1 s...

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LeetCode 84: Largest Rectangle in Histogram

Problem Restatement We are given an integer array heights . Each value represents the height of one bar in a histogram. Each bar has width 1 . We need to return the area of the largest rectangle that can be formed inside the histogram. The rectangle must use consecutive bars. Its height is limited by the shortest bar in that chosen range. The official statement gives heights = [2, 1,...

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LeetCode 456: 132 Pattern

Problem Restatement We are given an integer array nums . We need to determine whether there exists a subsequence of three elements: nums[i], nums[j], nums[k] such that: i < j < k and: nums[i] < nums[k] < nums[j] This is called a 132 pattern . The order of indices is 1 -> 3 -> 2 . The values must look like: small < middle < large but they appear in...

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LeetCode 255: Verify Preorder Sequence in Binary Search Tree

Problem Restatement We are given an array of unique integers called preorder . We need to decide whether this array could be the preorder traversal of a binary search tree. In preorder traversal, nodes are visited in this order: Visit root. Visit left subtree. Visit right subtree. For a binary search tree: Position Rule Left subtree Values are smaller than the root Right subtree Values are larger than the root...

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LeetCode 402: Remove K Digits

Problem Restatement We are given a string num representing a non-negative integer and an integer k . We must remove exactly k digits from num . After removing those digits, the remaining digits must stay in their original relative order. Return the smallest possible integer as a string. The result should not contain leading zeroes. If all digits are removed, or the remaining number becomes empty after removing leading zeroes,...

#monotonic-stack

LeetCode 3430 - Maximum and Minimum Sums of at Most Size K Subarrays

LeetCode 3878 - Count Good Subarrays

LeetCode 3816 - Lexicographically Smallest String After Deleting Duplicate Characters

LeetCode 3555 - Smallest Subarray to Sort in Every Sliding Window

LeetCode 3676 - Count Bowl Subarrays

LeetCode 3638 - Maximum Balanced Shipments

LeetCode 3542 - Minimum Operations to Convert All Elements to Zero

LeetCode 3523 - Make Array Non-decreasing

LeetCode 3420 - Count Non-Decreasing Subarrays After K Operations

LeetCode 2487 - Remove Nodes From Linked List

LeetCode 3205 - Maximum Array Hopping Score I

LeetCode 3221 - Maximum Array Hopping Score II

LeetCode 1856 - Maximum Subarray Min-Product

LeetCode 3229 - Minimum Operations to Make Array Equal to Target

LeetCode 2866 - Beautiful Towers II

LeetCode 1996 - The Number of Weak Characters in the Game

LeetCode 2617 - Minimum Number of Visited Cells in a Grid

LeetCode 2818 - Apply Operations to Maximize Score

LeetCode 2104 - Sum of Subarray Ranges

LeetCode 2030 - Smallest K-Length Subsequence With Occurrences of a Letter

LeetCode 1950 - Maximum of Minimum Values in All Subarrays

LeetCode 3359 - Find Sorted Submatrices With Maximum Element at Most K

LeetCode 2736 - Maximum Sum Queries

LeetCode 2297 - Jump Game VIII

LeetCode 2289 - Steps to Make Array Non-decreasing

LeetCode 2355 - Maximum Number of Books You Can Take

LeetCode 2281 - Sum of Total Strength of Wizards

LeetCode 2282 - Number of People That Can Be Seen in a Grid

LeetCode 2940 - Find Building Where Alice and Bob Can Meet

LeetCode 2865 - Beautiful Towers I

LeetCode 2832 - Maximal Range That Each Element Is Maximum in It

LeetCode 2345 - Finding the Number of Visible Mountains

LeetCode 3113 - Find the Number of Subarrays Where Boundary Elements Are Maximum

LeetCode 1944 - Number of Visible People in a Queue

LeetCode 2334 - Subarray With Elements Greater Than Varying Threshold

LeetCode 2863 - Maximum Length of Semi-Decreasing Subarrays

LeetCode 1966 - Binary Searchable Numbers in an Unsorted Array

LeetCode 2454 - Next Greater Element IV

LeetCode 2945 - Find Maximum Non-decreasing Array Length

LeetCode 901 - Online Stock Span

LeetCode 1475 - Final Prices With a Special Discount in a Shop

LeetCode 84 - Largest Rectangle in Histogram

LeetCode 1526 - Minimum Number of Increments on Subarrays to Form a Target Array

LeetCode 739 - Daily Temperatures

LeetCode 456 - 132 Pattern

LeetCode 1574 - Shortest Subarray to be Removed to Make Array Sorted

LeetCode 1762 - Buildings With an Ocean View

LeetCode 316 - Remove Duplicate Letters

LeetCode 1776 - Car Fleet II

LeetCode 1081 - Smallest Subsequence of Distinct Characters

LeetCode 1019 - Next Greater Node In Linked List

LeetCode 853 - Car Fleet

LeetCode 975 - Odd Even Jump

LeetCode 1504 - Count Submatrices With All Ones

LeetCode 769 - Max Chunks To Make Sorted

LeetCode 1130 - Minimum Cost Tree From Leaf Values

LeetCode 321 - Create Maximum Number

LeetCode 1793 - Maximum Score of a Good Subarray

LeetCode 1124 - Longest Well-Performing Interval

LeetCode 255 - Verify Preorder Sequence in Binary Search Tree

LeetCode 42 - Trapping Rain Water

LeetCode 907 - Sum of Subarray Minimums

LeetCode 1063 - Number of Valid Subarrays

LeetCode 581 - Shortest Unsorted Continuous Subarray

LeetCode 1008 - Construct Binary Search Tree from Preorder Traversal

LeetCode 85 - Maximal Rectangle

LeetCode 503 - Next Greater Element II

LeetCode 496 - Next Greater Element I

LeetCode 402 - Remove K Digits

LeetCode 768 - Max Chunks To Make Sorted II

LeetCode 962 - Maximum Width Ramp

LeetCode 1673 - Find the Most Competitive Subsequence

LeetCode 654 - Maximum Binary Tree

LeetCode 1019: Next Greater Node In Linked List

LeetCode 1063: Number of Valid Subarrays

LeetCode 1081: Smallest Subsequence of Distinct Characters

LeetCode 975: Odd Even Jump

LeetCode 768: Max Chunks To Make Sorted II

LeetCode 962: Maximum Width Ramp