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Largest Rectangle in Histogram⚓︎

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Description⚓︎

Given an array of integers heights representing the histogram's bar height where the width of each bar is 1, return the area of the largest rectangle in the histogram.

Example 1:

Ex1

  • Input: heights = [2,1,5,6,2,3]
  • Output: 10
  • Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area, which has an area = 10 units.

Example 2:

Ex2

  • Input: heights = [2,4]
  • Output: 4

Constraints:

  • 1 <= heights.length <= 10^5
  • 0 <= heights[i] <= 10^4

Solution⚓︎

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class Solution {
public:
    int largestRectangleArea(vector<int>& heights) {
        int n = heights.size();
        int res = 0;
        stack<int> stk;
        for (int i = 0; i < n; i++) {
            while (!stk.empty() && heights[stk.top()] >= heights[i]) {
                int current = stk.top();
                stk.pop();
                int left = !stk.empty() ? stk.top() : -1;
                res = max(res, heights[current] * (i - left - 1));
            }
            stk.push(i);
        }

        while (!stk.empty()) {
            int current = stk.top();
            stk.pop();
            int left = !stk.empty() ? stk.top() : -1;
            res = max(res, heights[current] * (n - left - 1));
        }

        return res;
    }
};