Trapping Rain Water

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.

The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image!

Analysis

• Note: need more thinking!!

Code

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

Reference

Similar idea, Yu's is clearer to me.

• Leetcode
• Yu