Leetcode 42: 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!

 

public class Solution {
    public int Trap(int[] height) {
        if (height.Length <= 1) return 0;
        
        var leftHighest = new int[height.Length];
        
        var curMax = 0;
        for (int i = 0; i < height.Length; i++)
        {
            curMax = Math.Max(curMax, height[i]);
            leftHighest[i] = curMax;
        }
        
        var result = 0;
        curMax = 0;      
        
        for (int i = height.Length - 1; i >= 0; i--)
        {
            curMax = Math.Max(curMax, height[i]);
            if (curMax > height[i] && leftHighest[i] > height[i])
            {
                result = result + Math.Min(curMax, leftHighest[i]) - height[i];
            }
        }
        
        return result;
    }
}