3Sum Closest

本文转载自：http://blog.csdn.net/doc_sgl/article/details/12461893

Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

For example, given array S = {-1 2 1 -4}, and target = 1.    The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

1. int threeSumClosest(vector<int> &num, int target) {  
2.         // Start typing your C/C++ solution below  
3.         // DO NOT write int main() function  
4.         int numlen = num.size();  
5.         if(numlen<3)return -1;  
6.   
7.         sort(num.begin(),num.end());  
8.         int minGap = num[0]+num[1]+num[2]-target;  
9.         for(int i = 0; i <= numlen-3; i++)  
10.         {  
11.             int begin = i+ 1;  
12.             int end = numlen-1;  
13.             while(begin < end)  
14.             {  
15.                 int curGap = num[i]+num[begin]+num[end]-target;  
16.                 if(curGap == 0) return target;  
17.                 if(abs(curGap) < abs(minGap)) minGap = curGap;  
18.                 if(curGap < 0)   begin++;  
19.                 else end--;  
20.             }  
21.         }  
22.         return target+minGap;  
23.     }