3Sum Closest

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.

没啥fancy的，sort完事了就行了。。。本来还想优化的，和3sum一样整一遍完事了。。。

class Solution {
public:
    int threeSumClosest(vector<int> &num, int target) {
      sort(num.begin(),num.end());
      int size=num.size();
      int res=num[0]+num[1]+num[size-1];
      for (int i=0; i<size;i++){
	int begin=i+1;
	int end=size-1;

	while(begin<end){
	  int sum=num[i]+num[begin]+num[end];
	  if (abs(target-sum)<abs(target-res)){
	    res=sum;
	  }
	  if (sum==target)
	    return sum;
	  if (sum>target)
	    end--;
	  if (sum<target)
	    begin++;
	}
      }
      return res;
    }
};