16 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).

Solution

class Solution {
public:
    int threeSumClosest(vector<int>& nums, int target) {
        sort(nums.begin(), nums.end());
        int diff = INT_MAX, sum, c_sum;
        int n = nums.size();
        if ( n <= 2 ) return 0;
        for ( int i = 0; i <= n-3; i++ ) {
            int j = i+1, k = n-1;
            while ( j <= k-1 ) {
                sum = nums[i] + nums[j] + nums[k];
                if ( sum == target ) return sum;
                if ( sum > target )  {
                    if ( diff > sum-target ) { diff = sum - target; c_sum = sum; }
                    k -= 1;
                }
                if ( sum < target ) {
                    if ( diff > target - sum ) { diff = target - sum; c_sum = sum; }
                    j += 1;
                }
            }
        }
        return c_sum;
    }
};