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).

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int n = nums.size();
        if(n < 3)   return INT_MIN;

        int gap = INT_MAX;
        int res = 0;
        sort(nums.begin(), nums.end());

        for(int i = 0; i < n - 2; i++){
            int j = i + 1;
            int k = n - 1;

            while(j < k){
                int sum = nums[i] + nums[j] + nums[k];

                if(abs(sum - target) < gap){
                    gap = abs(sum- target);
                    res = sum;
                }

                if(sum < target)
                    j++;
                else
                    k--;
            }
        }

        return res;
    }
};