leetcode/LC84_LargestRectangleInHistogram.java at main · ganeshakkimardi/leetcode · GitHub

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package practise.src.main.java.leetCode;

import java.util.Stack;

public class LC84_LargestRectangleInHistogram {
    public static void main(String[] args) {
        int[] heights = {2,1,5,6,2,3};
        System.out.println(largestRectangleArea(heights));
    }

    private static int largestRectangleArea(int[] heights) {
        int n = heights.length;
        int[] left = new int[n];
        int[] right = new int[n];

        left[0] = -1;
        for (int i = 1; i < n; i++) {
            int j = i - 1;
            while (j >= 0 && heights[j] >= heights[i]) {
                j = left[j];
            }
            left[i] = j;
        }

        right[n - 1] = n;
        for (int i = n - 2; i >= 0; i--) {
            int j = i + 1;
            while (j < n && heights[j] >= heights[i]) {
                j = right[j];
            }
            right[i] = j;
        }

        int maxArea = 0;
        for (int i = 0; i < n; i++) {
            int width = right[i] - left[i] - 1;
            maxArea = Math.max(maxArea, heights[i] * width);
        }

        return maxArea;
    }
}