Largest Rectangle in Histogram

Author: TonyStark-19

Stack/LargestRectangleInHistogram.cpp

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+#include <iostream>
+#include <stack>
+#include <vector>
+using namespace std;
+
+int largestRectangleArea(vector<int> &heights)
+{
+    int n = heights.size();
+    vector<int> left(n, 0);  // left smaller nearst
+    vector<int> right(n, 0); // right smaller nearst
+    stack<int> s;
+
+    // right smaller
+    for (int i = n - 1; i >= 0; i--)
+    {
+        while (s.size() > 0 && heights[s.top()] >= heights[i]) // removing invlaid values
+        {
+            s.pop();
+        }
+
+        right[i] = s.empty() ? n : s.top();
+
+        s.push(i);
+    }
+
+    while (!s.empty()) // to remove previous stack element
+    {
+        s.pop();
+    }
+
+    // left smaller
+    for (int i = 0; i < n; i++)
+    {
+        while (s.size() > 0 && heights[s.top()] >= heights[i]) // removing invlaid values
+        {
+            s.pop();
+        }
+
+        left[i] = s.empty() ? -1 : s.top();
+
+        s.push(i);
+    }
+
+    int ans = 0;
+    for (int i = 0; i < n; i++)
+    {
+        int width = right[i] - left[i] - 1;
+        int currArea = heights[i] * width;
+        ans = max(ans, currArea);
+    }
+
+    return ans;
+}
+
+int main()
+{
+    vector<int> arr = {2, 1, 5, 6, 2, 3};
+
+    cout << largestRectangleArea(arr) << endl;
+
+    return 0;
+}