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).

public int ThreeSumClosest(int[] nums, int target) {
        Array.Sort(nums);
        int size = nums.Count();
        int res = Int32.MaxValue;
        for(int i =0;i< size-1;i++)
        {
            int last = Int32.MaxValue;
            int dif = target - nums[i];
            int left = i+1;
            int right = size-1;
            while(left < right)
            {
                int a = nums[left] + nums[right] - dif;
                if(a==0) return target;
                if(Math.Abs(a)< last )
                {
                    res = Math.Abs(a)>Math.Abs(res) ?res :a;
                    last = Math.Abs(a);
                }
                if(a<0) left++;
                else right--;
            }
            
        }
        return res+target;
    }