题目：

题解：

class Solution {
public:int trap(vector<int>& height) {int n = height.size();if (n == 0) {return 0;}vector<int> leftMax(n);leftMax[0] = height[0];for (int i = 1; i < n; ++i) {leftMax[i] = max(leftMax[i - 1], height[i]);}vector<int> rightMax(n);rightMax[n - 1] = height[n - 1];for (int i = n - 2; i >= 0; --i) {rightMax[i] = max(rightMax[i + 1], height[i]);}int ans = 0;for (int i = 0; i < n; ++i) {ans += min(leftMax[i], rightMax[i]) - height[i];}return ans;}
};