84. Largest Rectangle in Histogram

Hard

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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:

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:

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

Constraints:

• 1 <= heights.length <= 105

• 0 <= heights[i] <= 104

class Solution:
    def largestRectangleArea(self, heights: List[int]) -> int:
        heights.append(0) # This 0 helps in cases like [1,2,3,4,5]
        stack = [-1]
        result = 0
        for index in range(len(heights)):
            # If Current Height Less Than Top Height of Stack
            while heights[index] < heights[stack[-1]]:
                h = heights[stack.pop()]
                # print('Height', h)
                w = index -1 - stack[-1]
                result = max(result, h*w)
            stack.append(index)
        return resultpy