1class Solution {2    public int trap(int[] height) {3        int left = 0, right = height.length - 1;4        int leftMax = 0, rightMax = 0, water = 0;5        while (left <= right) {6            if (height[left] <= height[right]) {7                leftMax = Math.max(leftMax, height[left]);8                water += leftMax - height[left];9                left++;10            } else {11                rightMax = Math.max(rightMax, height[right]);12                water += rightMax - height[right];13                right--;14            }15        }16        return water;17    }18}