[Leetcode] Trapping Rain Water

Trapping Rain WaterMar 10 '124164 / 10550

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

这题之前面试时遇到过类似的。

但是是二维的情况，当时想得比较混乱。后来网上看到了不错的做法：从边界开始，每次取边界上最矮的板作为往里面floodfill，遇到高的停止。

这题类似的处理，简单很多。

二维：http://www.cnblogs.com/liangfeng/archive/2011/09/19/2181695.html

class Solution {
public:
    int trap(int A[], int n) {
        int i = 0, j = n - 1, res = 0, cur;
        int *a = A;
        while (i < j) {
            if (a[i] < a[j]) {
                cur = i+1;
                while (cur <= j && a[cur] <= a[i]) res += a[i] - a[cur++];
                i = cur;
            } else {
                cur = j - 1;
                while (cur >= i && a[cur] <= a[j]) res += a[j] - a[cur--];
                j = cur;
            }
        }
        return res;
    }
};