Added Largest Rectangle in Histogram

Author: gahogg

Largest Rectangle in Histogram - Leetcode 84/Largest Rectangle in Histogram - Leetcode 84.cpp

@@ -0,0 +1,32 @@
+#include <vector>
+#include <stack>
+#include <algorithm>
+
+class Solution {
+public:
+    int largestRectangleArea(std::vector<int>& heights) {
+        int n = heights.size();
+        std::stack<std::pair<int, int>> stk;
+        int maxArea = 0;
+
+        for (int i = 0; i < n; i++) {
+            int height = heights[i];
+            int start = i;
+            while (!stk.empty() && height < stk.top().first) {
+                auto [h, j] = stk.top(); stk.pop();
+                int w = i - j;
+                maxArea = std::max(maxArea, h * w);
+                start = j;
+            }
+            stk.push({height, start});
+        }
+
+        while (!stk.empty()) {
+            auto [h, j] = stk.top(); stk.pop();
+            int w = n - j;
+            maxArea = std::max(maxArea, h * w);
+        }
+
+        return maxArea;
+    }
+};

Largest Rectangle in Histogram - Leetcode 84/Largest Rectangle in Histogram - Leetcode 84.java

@@ -0,0 +1,31 @@
+class Solution {
+    public int largestRectangleArea(int[] heights) {
+        int n = heights.length;
+        Stack<int[]> stk = new Stack<>();
+        int maxArea = 0;
+
+        for (int i = 0; i < n; i++) {
+            int height = heights[i];
+            int start = i;
+            while (!stk.isEmpty() && height < stk.peek()[0]) {
+                int[] popped = stk.pop();
+                int h = popped[0];
+                int j = popped[1];
+                int w = i - j;
+                maxArea = Math.max(maxArea, h * w);
+                start = j;
+            }
+            stk.push(new int[]{height, start});
+        }
+
+        while (!stk.isEmpty()) {
+            int[] popped = stk.pop();
+            int h = popped[0];
+            int j = popped[1];
+            int w = n - j;
+            maxArea = Math.max(maxArea, h * w);
+        }
+
+        return maxArea;
+    }
+}

Largest Rectangle in Histogram - Leetcode 84/Largest Rectangle in Histogram - Leetcode 84.js

@@ -0,0 +1,26 @@
+var largestRectangleArea = function(heights) {
+    var n = heights.length;
+    var stk = [];
+    var maxArea = 0;
+
+    for (var i = 0; i < n; i++) {
+        var height = heights[i];
+        var start = i;
+        while (stk.length > 0 && height < stk[stk.length - 1][0]) {
+            var [h, j] = stk.pop();
+            var w = i - j;
+            var a = h * w;
+            maxArea = Math.max(maxArea, a);
+            start = j;
+        }
+        stk.push([height, start]);
+    }
+
+    while (stk.length > 0) {
+        var [h, j] = stk.pop();
+        var w = n - j;
+        maxArea = Math.max(maxArea, h * w);
+    }
+
+    return maxArea;
+};

Largest Rectangle in Histogram - Leetcode 84/Largest Rectangle in Histogram - Leetcode 84.py

@@ -0,0 +1,24 @@
+class Solution:
+    def largestRectangleArea(self, heights: List[int]) -> int:
+        n = len(heights)
+        stk = []
+        max_area = 0
+
+        for i, height in enumerate(heights):
+            start = i
+            while stk and height < stk[-1][0]:
+                h, j = stk.pop()
+                w = i - j
+                a = h*w
+                max_area = max(max_area, a)
+                start = j
+            stk.append((height, start))
+        
+        while stk:
+            h, j = stk.pop()
+            w = n - j
+            max_area = max(max_area, h*w)
+        
+        return max_area
+        # Time: O(n)
+        # Space: O(n)