42. Trapping Rain Water

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