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();
        sort(nums.begin(),nums.end());
        int differ=INT_MAX;
        int res=0;
        for(int i=0;i<n-2;i++){
            int left=i+1;
            int right=n-1;
            int sum=0;
            while(left<right){
                sum=nums[i]+nums[left]+nums[right];
                if(sum==target) return target;
                else if(sum<target){
                    if(target-sum<differ){
                        differ=target-sum;
                        res=sum;
                    }
                    left++;
                }else{
                    if(sum-target<differ){
                        differ=sum-target;
                        res=sum;
                    }
                    right--;
                }
            }
            while(nums[i]==nums[i+1]) i++;
        }
        return res;
    }
};