Review Note

• 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.
  

class Solution:
    def largestRectangleArea(self, heights: List[int]) -> int:
        maxArea = 0
        stack = [] # (i, height)
        heights.append(0)
        for i, height in enumerate(heights):
            start = i
            while stack and height < stack[-1][1]:
                iPrev, heightPrev = stack.pop()
                maxArea  = max(maxArea, heightPrev * (i - iPrev))
                start = iPrev
            stack.append((start, height))
        return maxArea