84. 柱状图中最大的矩形

1. 题目链接

2. 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

3. 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