84. 柱状图中最大的矩形

题目链接

解题思路：单调栈，以i位置为高度(宽)，最长能有多长，其实就是找离i最近的，小于i的位置，其实就是单调栈

代码

class Solution:
    def largestRectangleArea(self, heights: List[int]) -> int:
        # 使用单调栈   栈底到栈顶   小到大
        stack = []
        ans = 0
        n = len(heights)
        for i in range (n): 
            while stack and heights[stack[-1]] > heights[i]:
                cur = stack.pop()
                R = i
                L = 0
                if stack:
                    L = stack[-1] + 1
                ans = max(ans, (R - L) * heights[cur])
            stack.append(i)
        while stack:
            cur = stack.pop()
            R = n
            L = 0
            if stack:
                L = stack[-1] + 1
            ans = max(ans, (R - L) * heights[cur])
        return ans