LeetCode 3Sum Closest

题目：

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).

class Solution {
public:
int threeSumClosest(vector<int> &num, int target) {
int minVal = INT_MAX;
int len = num.size();
sort(num.begin(), num.end());
int ans, sum;
for(int i = 0; i < len-2; i++) {
int begin = i+1, end = len-1;
while(begin < end) {
sum = num[i] + num[begin] + num[end];
if(abs(sum-target) < minVal) {
minVal = abs(sum-target);
ans = sum;
}
if(sum == target)
return ans;
else if(sum < target)
begin++;
else
end--;

}
}
return ans;
}
};