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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!

C++实现代码:

#include<iostream>using namespace std;class Solution {public:     // 关键是在于找到规律:      // 即第i块地方的存水量 = min(第i块左边最高的bar高度, 第i块右边最高的bar的高度) - 第i块地方bar的高度      // 例如图中,第5块地方的存水量 = min(2,3)-0 = 2      // 2为其左边最高的bar,即第3块地方的bar      // 3为其右边最高的bar,即第7块地方的bar,      // 0为其自身的bar高度     int trap(int A[], int n) {        if(n==0)            return 0;        int left[n];        int right[n];        int i;        int sum=0;        left[0]=A[0];        for(i=1;i<n;i++)            left[i]=max(left[i-1],A[i]);        right[n-1]=A[n-1];        for(i=n-2;i>=0;i--)            right[i]=max(right[i+1],A[i]);        for(i=1;i<n-1;i++)            sum+=(min(left[i],right[i])-A[i]);        return sum;    }};int main(){    Solution s;    int A[12]={0,1,0,2,1,0,1,3,2,1,2,1};    cout<<s.trap(A,12)<<endl;}

参考:http://blog.csdn.net/fightforyourdream/article/details/15026089

Trapping Rain Water