Leetcode: 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.

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).

int threeSumClosest(vector<int> &num, int target) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int numlen = num.size();
if(numlen<3)return -1;

sort(num.begin(),num.end());
int minGap = num[0]+num[1]+num[2]-target;
for(int i = 0; i <= numlen-3; i++)
{
int begin = i+ 1;
int end = numlen-1;
while(begin < end)
{
int curGap = num[i]+num[begin]+num[end]-target;
if(curGap == 0)	return target;
if(abs(curGap) < abs(minGap)) minGap = curGap;
if(curGap < 0)	begin++;
else end--;
}
}
return target+minGap;
}