leetcode 3sum closest

class  {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        int res = 0;
        int min_gap = INT_MAX;
        sort(nums.begin(), nums.end());
        auto last = nums.end();
        for(auto i = nums.begin(); i < last - 2; ++i) {
            auto j = next(i);
            auto k = last - 1;
            while(j < k) {
                const int sum = *i + *j + *k;
                const int gap = abs(sum - target);
                if(gap < min_gap) {
                    min_gap = gap;
                    res = sum;
                }
                if(sum > target) {
                    k--;
                }else {
                    j++;
                }
            }
        }
        return res;        
    }
};