From 4635eeef27a3e69990f8f950030c47ca19a3056c Mon Sep 17 00:00:00 2001
From: vivek-kumar-gupta <wisdom655@gmail.com>
Date: Wed, 26 Apr 2023 03:04:50 +0530
Subject: [PATCH 1/4] Update 0084-largest-rectangle-in-histogram.java

---
 java/0084-largest-rectangle-in-histogram.java | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/java/0084-largest-rectangle-in-histogram.java b/java/0084-largest-rectangle-in-histogram.java
index 6ba5e0303..d2aeb3bbf 100644
--- a/java/0084-largest-rectangle-in-histogram.java
+++ b/java/0084-largest-rectangle-in-histogram.java
@@ -1,3 +1,6 @@
+//Please check this video which has best explaination which is understandable.
+//https://youtu.be/lJLcqDsmYfg
+
 class Solution {
     public int largestRectangleArea(int[] heights) {
       int area = 0, n = heights.length;

From b00a0df82ad9839e65753afbb1d8247eeb5b43f7 Mon Sep 17 00:00:00 2001
From: vivek-kumar-gupta <wisdom655@gmail.com>
Date: Wed, 26 Apr 2023 03:43:11 +0530
Subject: [PATCH 2/4] Update 0084-largest-rectangle-in-histogram.java

---
 java/0084-largest-rectangle-in-histogram.java | 52 +++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/java/0084-largest-rectangle-in-histogram.java b/java/0084-largest-rectangle-in-histogram.java
index d2aeb3bbf..54445895d 100644
--- a/java/0084-largest-rectangle-in-histogram.java
+++ b/java/0084-largest-rectangle-in-histogram.java
@@ -1,6 +1,58 @@
 //Please check this video which has best explaination which is understandable.
 //https://youtu.be/lJLcqDsmYfg
 
+class Solution2 {
+    public int largestRectangleArea(int[] heights) {
+
+        int[] nextSmallerIndices = findNextSmallerIndex(heights);
+        int[] prevSmallerIndices = findPrevSmallerIndex(heights);
+        int maxArea = 0;
+        for (int i = 0; i < heights.length; i++){
+
+            maxArea = Math.max(maxArea, ((nextSmallerIndices[i] == - 1 
+            ? heights.length : nextSmallerIndices[i]) - prevSmallerIndices[i] - 1) * heights[i]);
+        }
+        return maxArea;
+    }
+
+
+    private int[] findNextSmallerIndex(int[] heights){
+        Stack<Integer> stack = new Stack<>();
+        int[] result = new int[heights.length];
+        stack.push(-1);
+
+        for (int i = heights.length - 1; i >=0 ; i--){
+           while (stack.peek() != -1 && heights[stack.peek()] >= heights[i]){
+                  stack.pop();
+            }
+
+            result[i] = stack.peek();
+            stack.push(i);
+            
+
+        }
+        return result;
+
+    }
+
+    private int[] findPrevSmallerIndex(int[] heights){
+        Stack<Integer> stack = new Stack<>();
+        int[] result = new int[heights.length];
+        stack.push(-1);
+
+        for (int i = 0; i < heights.length ; i++){
+            while (stack.peek() != -1 && heights[stack.peek()] >= heights[i]){
+                  stack.pop();
+            }
+            result[i] = stack.peek();
+            stack.push(i);
+            
+
+        }
+        return result;
+    }
+}
+
 class Solution {
     public int largestRectangleArea(int[] heights) {
       int area = 0, n = heights.length;

From f31756c0e5b9fd97feb11e79288f5296e1888cb4 Mon Sep 17 00:00:00 2001
From: vivek-kumar-gupta <wisdom655@gmail.com>
Date: Thu, 27 Apr 2023 01:59:05 +0530
Subject: [PATCH 3/4] Update 0424-longest-repeating-character-replacement.java

---
 java/0424-longest-repeating-character-replacement.java | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/java/0424-longest-repeating-character-replacement.java b/java/0424-longest-repeating-character-replacement.java
index 1ce9988b4..4845307a0 100644
--- a/java/0424-longest-repeating-character-replacement.java
+++ b/java/0424-longest-repeating-character-replacement.java
@@ -1,5 +1,8 @@
 class Solution {
 
+    
+    //Please see the way sliding window is implemented.
+    // This is goood as if you go for other way.. will be bit confusing and time consuming.
     public int characterReplacement(String s, int k) {
         int[] arr = new int[26];
         int ans = 0;

From 8afa89059e07ce8f580bfcf783e684246ff85af6 Mon Sep 17 00:00:00 2001
From: vivek-kumar-gupta <wisdom655@gmail.com>
Date: Thu, 27 Apr 2023 03:09:43 +0530
Subject: [PATCH 4/4] Update 0239-sliding-window-maximum.java

---
 java/0239-sliding-window-maximum.java | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/java/0239-sliding-window-maximum.java b/java/0239-sliding-window-maximum.java
index f4acef438..42bd654ab 100644
--- a/java/0239-sliding-window-maximum.java
+++ b/java/0239-sliding-window-maximum.java
@@ -1,11 +1,13 @@
 class Solution {
-
+    //It also has nice explainasion.
     public int[] maxSlidingWindow(int[] nums, int k) {
         int[] ans = new int[nums.length - k + 1];
         int j = 0;
         Deque<Integer> q = new LinkedList<>();
         for (int i = 0; i < nums.length; i++) {
+            //here we are checking if this is in current bound if not removing it.
             if (!q.isEmpty() && q.peekFirst() < i - k + 1) q.pollFirst();
+            //here we are checking if current element is greater than value in queue.. then keep polling it.
             while (!q.isEmpty() && nums[i] > nums[q.peekLast()]) q.pollLast();
             q.offer(i);
             if (i >= k - 1) ans[j++] = nums[q.peekFirst()];