[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).

class Solution {
public:
    int threeSumClosest(vector<int> &num, int target) {
        sort(num.begin(), num.end());
        
        int diff = INT_MAX; 
        int res = 0;
        
        for(int i=0;i<num.size()-2;i++)
        {
            if(i && num[i] == num[i-1]) continue;
            int start = i + 1;
            int end = num.size() - 1;

            while(start < end)
            {
                int sum = num[start] + num[end] + num[i];

                if(sum == target)
                {
                    return target;
                }
                int k = abs(sum-target);
                if(k < diff)
                {
                    diff = k;
                    res = sum;
                }
                
                sum > target ? end-- : start++;
                
            }
        }
        
        return res;
    }
};