/*
 * @lc app=leetcode id=42 lang=java
 *
 * [42] Trapping Rain Water
 */

// @lc code=start
class Solution {
    public int trap(int[] height) {
        int lmax = height[0], rmax = height[height.length-1];
        int l = 0, r = height.length-1, cap = 0;
        while(l <= r) {
            if(lmax < rmax) {
                cap += lmax - height[l];
                l++;
                if(l < height.length) {
                    lmax = Math.max(lmax, height[l]);
                }
            } else {
                cap += rmax - height[r];
                r--;
                if(r >=0) {
                    rmax = Math.max(rmax, height[r]);
                }
            }
        }
        return cap;
    }
}
// @lc code=end