Trapping Rain Water

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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!

int trap(vector<int>& height) {
     int l = 0, r = height.size()-1, level = 0, water = 0;
        while (l < r) {
            int lower = height[height[l] < height[r] ? l++ : r--];
            cout<<"level: "<<level<<"   lower: " <<lower<<endl;
            level = max(level, lower);//level始终存放安全高度，lower存放当前最低高度，
            water += level - lower;
            cout<<"w: "<<water<<endl;
        }
        return water;
}

Trapping Rain Water

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原文地址：http://www.cnblogs.com/wqkant/p/5376439.html