题目：

题解:

func trap(height []int) (ans int) {n := len(height)if n == 0 {return}leftMax := make([]int, n)leftMax[0] = height[0]for i := 1; i < n; i++ {leftMax[i] = max(leftMax[i-1], height[i])}rightMax := make([]int, n)rightMax[n-1] = height[n-1]for i := n - 2; i >= 0; i-- {rightMax[i] = max(rightMax[i+1], height[i])}for i, h := range height {ans += min(leftMax[i], rightMax[i]) - h}return
}func min(a, b int) int {if a < b {return a}return b
}func max(a, b int) int {if a > b {return a}return b
}