leetcode-84-柱状图中最大的矩形

题目描述：

 

 方法一：O(N) O(N)

class Solution:
    def largestRectangleArea(self, heights: List[int]) -> int:
        if not heights:
            return 0
        n = len(heights)
        left_i = [0] * n
        right_i = [0] * n
        left_i[0] = -1
        right_i[-1] = n
        for i in range(1, n):
            tmp = i - 1
            while tmp >= 0 and heights[tmp] >= heights[i]:
                tmp = left_i[tmp]
            left_i[i] = tmp
        for i in range(n - 2, -1, -1):
            tmp = i + 1
            while tmp < n and heights[tmp] >= heights[i]:
                tmp = right_i[tmp]
            right_i[i] = tmp
        # print(left_i)
        # print(right_i)
        res = 0
        for i in range(n):
            res = max(res, (right_i[i] - left_i[i] - 1) * heights[i])
        return res

方法二：栈 O(N)

class Solution:
    def largestRectangleArea(self, heights: List[int]) -> int:
        stack = []
        heights = [0] + heights + [0]
        res = 0
        for i in range(len(heights)):
            #print(stack)
            while stack and heights[stack[-1]] > heights[i]:
                tmp = stack.pop()
                res = max(res, (i - stack[-1] - 1) * heights[tmp])
            stack.append(i)
        return res