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美丽塔 II（前缀和 + 单调栈）

链接

class Solution:
    def maximumSumOfHeights(self, maxHeights: List[int]) -> int:
        n = len(maxHeights)
        stack = collections.deque()
        pre, suf = [0] * n, [0] * n
        for i in range(n):
            while stack and maxHeights[stack[-1]] > maxHeights[i]:
                stack.pop()
            if not stack:
                pre[i] = (i + 1) * maxHeights[i]
            else:
                pre[i] = pre[stack[-1]] + (i - stack[-1]) * maxHeights[i]
            stack.append(i)
        ans = 0
        stack.clear()
        for i in range(n - 1, -1, -1):
            while stack and maxHeights[stack[-1]] > maxHeights[i]:
                stack.pop()
            if not stack:
                suf[i] = (n - i) * maxHeights[i]
            else:
                suf[i] = suf[stack[-1]] + (stack[-1] - i) * maxHeights[i]
            stack.append(i)
            ans = max(ans, suf[i] + pre[i] - maxHeights[i])
        return ans