leetcode 84. Largest Rectangle in Histogram

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Given n non-negative integers representing the histogram’s bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.

image

Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].

image

The largest rectangle is shown in the shaded area, which has area = 10unit.

For example,
Given heights = [2,1,5,6,2,3],
return 10.

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class Solution(object):
    def largestRectangleArea(self, heights):
        """
        :type heights: List[int]
        :rtype: int
        """
        heights.append(0)
        stack = [-1]
        ans = 0
        for i in range(len(heights)):
            while heights[i] < heights[stack[-1]]:
                h = heights[stack.pop()]
                w = i - stack[-1] - 1
                ans = max(ans,w*h)
            stack.append(i)
        return ans