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Practice › Codeforces Solutions › Spectral::Cup 2026 Round 1 (Codeforces Round 1094, Div. 1 + Div. 2) ›

CF 2222E - Seek the Truth

CF 2222E - Seek the Truth Rating: - Tags: binary search, bitmasks, constructive algorithms, interactive Solve time: 1m 59s Verified: no Solution Problem Understanding The original problem is interactive, but the version used for judging after the contest is the hacked format. Instead of interacting with a judge, each test case directly gives us the hidden values n , k , and c . The interactive story is useful because...

Practice › Codeforces Solutions › Codeforces Round 945 (Div. 2) ›

CF 1973D - Cat, Fox and Maximum Array Split

CF 1973D - Cat, Fox and Maximum Array Split Rating: 2400 Tags: brute force, interactive, math Solve time: 5m 14s Verified: no Solution

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3094 - Guess the Number Using Bitwise Questions II

LeetCode Problem 3094 Difficulty: 🟡 Medium Topics: Bit Manipulation, Interactive Solution Before I write the full guide, I want to confirm one detail: for LeetCode 3094 - Guess the Number Using Bitwise Questions II , there are no public input/output examples in the problem statement because it is an interactive problem . I can still provide the complete reference guide with all requested sections, including: Problem Understanding Brute Force and...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3037 - Find Pattern in Infinite Stream II

LeetCode Problem 3037 Difficulty: 🔴 Hard Topics: Array, Sliding Window, Rolling Hash, String Matching, Interactive, Hash Function Solution Problem Understanding The problem requires us to detect the first occurrence of a binary pattern within a theoretically infinite stream of bits. The stream is accessed sequentially using the next() method, which returns one bit at a time. Our task is to determine the index in the stream where the given pattern...

Practice › LeetCode › LeetCode 29xx ›

LeetCode 2936 - Number of Equal Numbers Blocks

LeetCode Problem 2936 Difficulty: 🟡 Medium Topics: Array, Binary Search, Interactive Solution Problem Understanding The problem is asking us to count the number of maximal contiguous blocks of equal numbers in a very large array nums . A block is maximal if it contains all consecutive occurrences of the same number, and numbers are guaranteed to appear in consecutive segments, i.e., the array is already "grouped" by value. The key...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3064 - Guess the Number Using Bitwise Questions I

LeetCode Problem 3064 Difficulty: 🟡 Medium Topics: Bit Manipulation, Interactive Solution Problem Understanding The problem presents an interactive scenario where there is a hidden number n in the range [1, 2^30 - 1] . We are provided with an API commonSetBits(num) which returns the count of bits that are set in both n and num when performing a bitwise AND. In other words, commonSetBits(num) computes the number of positions where...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2782 - Number of Unique Categories

LeetCode Problem 2782 Difficulty: 🟡 Medium Topics: Union-Find, Interactive, Counting Solution Problem Understanding This problem asks us to determine how many distinct categories exist among n elements. The elements are labeled from 0 to n - 1 , but we are not given the category values directly. Instead, we interact with the hidden categorization through the provided API: haveSameCategory(a, b) This function tells us whether two elements belong to the...

Practice › LeetCode › LeetCode 27xx ›

LeetCode 2728 - Count Houses in a Circular Street

LeetCode Problem 2728 Difficulty: 🟢 Easy Topics: Array, Interactive Solution Problem Understanding The problem asks us to determine the number of houses on a circular street where we can only interact with the street through the provided Street interface. Each house has a door that can either be open or closed. We are initially positioned in front of one house, but we do not know which one, and the street...

Practice › LeetCode › LeetCode 30xx ›

LeetCode 3023 - Find Pattern in Infinite Stream I

LeetCode Problem 3023 Difficulty: 🟡 Medium Topics: Array, Sliding Window, Rolling Hash, String Matching, Interactive, Hash Function Solution Problem Understanding The problem asks us to detect the first occurrence of a given binary pattern within an infinite stream of bits. We are given an object stream that allows us to read one bit at a time using the next() function. Our task is to return the 0-based index in the...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 277 - Find the Celebrity

LeetCode Problem 277 Difficulty: 🟡 Medium Topics: Two Pointers, Graph Theory, Interactive Solution Problem Understanding This problem asks us to identify whether there is a "celebrity" among n people at a party. A celebrity has a very specific property: Every other person knows the celebrity. The celebrity knows nobody else. We are not given the entire relationship graph directly. Instead, we can only query relationships through the helper API: knows(a,...

Practice › LeetCode › LeetCode 16xx ›

LeetCode 1618 - Maximum Font to Fit a Sentence in a Screen

LeetCode Problem 1618 Difficulty: 🟡 Medium Topics: Array, String, Binary Search, Interactive Solution Problem Understanding In this problem, we are given a string text that must be displayed on a single line inside a screen with width w and height h . We are also given a sorted array fonts , where each value represents an available font size that we are allowed to use. The important detail is that...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1538 - Guess the Majority in a Hidden Array

LeetCode Problem 1538 Difficulty: 🟡 Medium Topics: Array, Math, Interactive Solution Problem Understanding This problem is an interactive problem. We do not receive the actual binary array directly. Instead, we can only gather information through the ArrayReader API. The hidden array nums contains only 0 and 1 . Our goal is to determine which value appears more frequently and return any index containing that majority value. If the number of...

Practice › LeetCode › LeetCode 14xx ›

LeetCode 1428 - Leftmost Column with at Least a One

LeetCode Problem 1428 Difficulty: 🟡 Medium Topics: Array, Binary Search, Matrix, Interactive Solution Problem Understanding This problem gives us access to a binary matrix where every row is sorted in non-decreasing order. That means every row looks like some number of 0 s followed by some number of 1 s. For example: [0, 0, 0, 1, 1] is valid, while: [0, 1, 0, 1] is not. The goal is to...

Practice › LeetCode › LeetCode 08xx ›

LeetCode 843 - Guess the Word

LeetCode Problem 843 Difficulty: 🔴 Hard Topics: Array, Math, String, Interactive, Game Theory Solution LeetCode 843 - Guess the Word Problem Understanding This is an interactive problem where we must identify a hidden six-letter word from a given list of candidate words. We are not allowed to directly inspect the secret word. Instead, we can interact with the provided Master API by calling master.guess(word) . Each call returns the number...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1274 - Number of Ships in a Rectangle

LeetCode Problem 1274 Difficulty: 🔴 Hard Topics: Array, Divide and Conquer, Interactive Solution Problem Understanding The problem presents an interactive scenario where ships are placed at integer coordinates on a Cartesian plane. You do not know their positions, and each coordinate contains at most one ship. You are given two points representing the bottom-left and top-right corners of a rectangle, and you need to determine the number of ships contained...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1236 - Web Crawler

LeetCode Problem 1236 Difficulty: 🟡 Medium Topics: String, Depth-First Search, Breadth-First Search, Interactive Solution Problem Understanding The problem asks us to implement a simplified web crawler. We are given a starting URL and access to an HtmlParser interface that can retrieve all URLs linked from a given webpage. Our task is to traverse the web graph beginning from startUrl , but with two important restrictions: We may only visit URLs...

Practice › LeetCode › LeetCode 12xx ›

LeetCode 1237 - Find Positive Integer Solution for a Given Equation

LeetCode Problem 1237 Difficulty: 🟡 Medium Topics: Math, Two Pointers, Binary Search, Interactive Solution Problem Understanding This problem gives us access to a hidden function f(x, y) through an interface. We are not allowed to know or implement the formula directly. Instead, we can only call the function with positive integers x and y and observe the result. The important property is that the function is strictly increasing in both...

Practice › LeetCode › LeetCode 18xx ›

LeetCode 1810 - Minimum Path Cost in a Hidden Grid

LeetCode Problem 1810 Difficulty: 🟡 Medium Topics: Array, Depth-First Search, Breadth-First Search, Graph Theory, Heap (Priority Queue), Matrix, Interactive, Shortest Path Solution Problem Understanding This problem is an interactive shortest path problem on a hidden weighted grid. We control a robot that starts somewhere in an unknown grid, and we must determine the minimum total movement cost required to reach a hidden target cell. Unlike a normal grid problem, we...

Practice › LeetCode › LeetCode 03xx ›

LeetCode 374 - Guess Number Higher or Lower

LeetCode Problem 374 Difficulty: 🟢 Easy Topics: Binary Search, Interactive Solution Problem Understanding The problem describes a classic interactive guessing game. A hidden number called pick is chosen somewhere in the range from 1 to n , inclusive. We are not allowed to access pick directly. Instead, we can only interact with the provided API function: guess(num) This API tells us whether our current guess is too high, too low,...

Practice › LeetCode › LeetCode 15xx ›

LeetCode 1533 - Find the Index of the Large Integer

LeetCode Problem 1533 Difficulty: 🟡 Medium Topics: Array, Binary Search, Interactive Solution Problem Understanding The problem presents an array arr where all elements are equal except for one element that is strictly larger than the others. However, we do not have direct access to the array elements. Instead, we interact with the array through an API called ArrayReader . This API provides two functions: compareSub(l, r, x, y) , which...

Practice › LeetCode › LeetCode 04xx ›

LeetCode 489 - Robot Room Cleaner

LeetCode Problem 489 Difficulty: 🔴 Hard Topics: Backtracking, Interactive Solution Problem Understanding This problem is an interactive backtracking problem where we must control a robot without directly seeing the room layout. Unlike traditional grid traversal problems, we are not given access to the actual room matrix during execution. The only way to explore the environment is through the robot's API. The room is conceptually a binary grid: 1 represents an...

Practice › LeetCode › LeetCode 10xx ›

LeetCode 1095 - Find in Mountain Array

LeetCode Problem 1095 Difficulty: 🔴 Hard Topics: Array, Binary Search, Interactive Solution Problem Understanding This problem gives us a special type of array called a mountain array. A mountain array strictly increases until it reaches a single peak element, then strictly decreases afterward. For example: 1 2 3 5 4 2 increases up to 5 , then decreases. The challenge is that this is an interactive problem. We cannot directly...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 157 - Read N Characters Given Read4

LeetCode Problem 157 Difficulty: 🟢 Easy Topics: Array, Simulation, Interactive Solution Problem Understanding This problem asks us to implement a read function using a restricted API called read4 . The file itself is hidden from us, and the only way to access its contents is by repeatedly calling read4 . The read4 API reads up to 4 consecutive characters from the file into a temporary buffer called buf4 . It...

Practice › LeetCode › LeetCode 01xx ›

LeetCode 158 - Read N Characters Given read4 II - Call Multiple Times

LeetCode Problem 158 Difficulty: 🔴 Hard Topics: Array, Simulation, Interactive Solution Problem Understanding This problem asks us to implement a read(buf, n) function using a restricted API called read4(buf4) . The challenge is that we are not allowed to access the file directly, instead, we can only retrieve data in chunks of up to four characters at a time. At first glance, this may look very similar to LeetCode 157,...

Practice › LeetCode › LeetCode 02xx ›

LeetCode 278 - First Bad Version

LeetCode Problem 278 Difficulty: 🟢 Easy Topics: Binary Search, Interactive Solution Problem Understanding The problem gives us a sequence of product versions numbered from 1 to n . At some point, one version becomes bad, and every version after it is also bad. This creates a monotonic pattern: Good versions appear first Bad versions appear afterward For example: Version: 1 2 3 4 5 Status : G G G B...

Practice › LeetCode › LeetCode 17xx ›

LeetCode 1778 - Shortest Path in a Hidden Grid

LeetCode Problem 1778 Difficulty: 🟡 Medium Topics: Array, Depth-First Search, Breadth-First Search, Matrix, Interactive Solution Problem Understanding This problem asks us to find the shortest path from a robot's unknown starting position to a hidden target inside a grid. The major challenge is that the grid itself is not directly accessible. Instead of receiving the matrix as input, we interact with the environment through a GridMaster API. The robot can...

Practice › LeetCode › LeetCode 07xx ›

LeetCode 702 - Search in a Sorted Array of Unknown Size

LeetCode Problem 702 Difficulty: 🟡 Medium Topics: Array, Binary Search, Interactive Solution Problem Understanding This problem asks us to search for a target value inside a sorted array, but with an important limitation: we do not know the size of the array, and we cannot access the array directly. Instead of normal array indexing, we interact with the array through an ArrayReader interface. The only available operation is: reader.get(index) This...

Practice › LeetCode › LeetCode (archived) › LeetCode 10xx ›

LeetCode 1095: Find in Mountain Array

Problem Restatement A mountain array increases to a peak and then decreases. We have access only through a MountainArray.get(index) API. We need to find the minimum index where mountainArr.get(index) == target . Return -1 if not found. We may call MountainArray.get() at most 100 times. The official constraints state that 3 <= mountainArr.length() <= 10^4 and all values are distinct. Input and Output Item Meaning Input MountainArray object and target...

Practice › LeetCode › LeetCode (archived) › LeetCode 08xx ›

LeetCode 843: Guess the Word

Problem Restatement We are given a list of unique strings words . Each word has length 6 . One word from the list is chosen as the secret word. We can call: master.guess(word) This returns: Return value Meaning -1 The guessed word is not in the word list 0 to 6 Number of positions where the guessed word matches the secret word We must find the secret word within at...

Practice › LeetCode › LeetCode (archived) › LeetCode 07xx ›

LeetCode 702: Search in a Sorted Array of Unknown Size

Problem Restatement We are given a sorted array, but we do not know its length. We cannot access the array directly. Instead, we can only use an ArrayReader interface: reader.get(index) This returns the value at index . If index is outside the array, reader.get(index) returns a very large sentinel value: 2147483647 We need to find the index of target . If target exists, return its index. If it does not...

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 158: Read N Characters Given read4 II - Call Multiple Times

Problem Restatement We are given a file, but we cannot read from it directly. The only available API is: read4(buf4) This reads up to 4 characters from the file into buf4 , then returns how many characters were actually read. We need to implement: read(buf, n) It should read up to n characters, write them into buf , and return the number of characters actually read. The difference from LeetCode...

Practice › LeetCode › LeetCode (archived) › LeetCode 02xx ›

LeetCode 278: First Bad Version

Problem Restatement We have versions numbered from 1 to n . At some version, the product becomes bad. Because each version is built from the previous one, every version after the first bad version is also bad. So the versions look like this: good, good, good, bad, bad, bad We are given an API: isBadVersion(version) It returns True if the version is bad and False if the version is good....

Practice › LeetCode › LeetCode (archived) › LeetCode 01xx ›

LeetCode 157: Read N Characters Given Read4

Problem Restatement We are given a file, but we cannot access the file directly. The only way to read from the file is through a provided API: read4(buf4) This function reads up to 4 characters from the file and writes them into buf4 . It returns the actual number of characters read. We need to implement: read(buf, n) This function should read up to n characters from the file, write...

Practice › LeetCode › LeetCode (archived) › LeetCode 02xx ›

LeetCode 277: Find the Celebrity

Problem Restatement There are n people at a party, labeled from 0 to n - 1 . A celebrity is a person who satisfies two conditions: Everyone else knows the celebrity. The celebrity knows nobody else. We are given an API: knows(a, b) It returns True if person a knows person b . We need to implement: findCelebrity(n) Return the celebrity label if one exists. Otherwise, return -1 . The...

#interactive

CF 2222E - Seek the Truth

CF 1973D - Cat, Fox and Maximum Array Split

LeetCode 3094 - Guess the Number Using Bitwise Questions II

LeetCode 3037 - Find Pattern in Infinite Stream II

LeetCode 2936 - Number of Equal Numbers Blocks

LeetCode 3064 - Guess the Number Using Bitwise Questions I

LeetCode 2782 - Number of Unique Categories

LeetCode 2728 - Count Houses in a Circular Street

LeetCode 3023 - Find Pattern in Infinite Stream I

LeetCode 277 - Find the Celebrity

LeetCode 1618 - Maximum Font to Fit a Sentence in a Screen

LeetCode 1538 - Guess the Majority in a Hidden Array

LeetCode 1428 - Leftmost Column with at Least a One

LeetCode 843 - Guess the Word

LeetCode 1274 - Number of Ships in a Rectangle

LeetCode 1236 - Web Crawler

LeetCode 1237 - Find Positive Integer Solution for a Given Equation

LeetCode 1810 - Minimum Path Cost in a Hidden Grid

LeetCode 374 - Guess Number Higher or Lower

LeetCode 1533 - Find the Index of the Large Integer

LeetCode 489 - Robot Room Cleaner

LeetCode 1095 - Find in Mountain Array

LeetCode 157 - Read N Characters Given Read4

LeetCode 158 - Read N Characters Given read4 II - Call Multiple Times

LeetCode 278 - First Bad Version

LeetCode 1778 - Shortest Path in a Hidden Grid

LeetCode 702 - Search in a Sorted Array of Unknown Size

LeetCode 1095: Find in Mountain Array

LeetCode 843: Guess the Word

LeetCode 702: Search in a Sorted Array of Unknown Size

LeetCode 158: Read N Characters Given read4 II - Call Multiple Times

LeetCode 278: First Bad Version

LeetCode 157: Read N Characters Given Read4

LeetCode 277: Find the Celebrity