42. Trapping Rain Water

Problem:

Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.

For example,
Given [0,1,0,2,1,0,1,3,2,1,2,1], return 6.

Analysis:

https://leetcode.com/problems/trapping-rain-water/solution/

Solution:

class Solution {
    public int trap(int[] height) {
        int left = 0;
        int right =  height.length - 1;
        int leftMax = 0;
        int rightMax = 0;
        int res = 0;
        while (left < right) {
            if (height[left] < height[right]) {
                leftMax = Math.max(leftMax, height[left]);
                res+= leftMax - height[left];
                left++;
            } else {
                rightMax = Math.max(rightMax, height[right]);
                res+= rightMax - height[right];
                right--;
            }
        }
        return res;
    }
}