题目：

题解：

class Solution:def trap(self, height: List[int]) -> int:if not height:return 0n = len(height)leftMax = [height[0]] + [0] * (n - 1)for i in range(1, n):leftMax[i] = max(leftMax[i - 1], height[i])rightMax = [0] * (n - 1) + [height[n - 1]]for i in range(n - 2, -1, -1):rightMax[i] = max(rightMax[i + 1], height[i])ans = sum(min(leftMax[i], rightMax[i]) - height[i] for i in range(n))return ans