Three Sum 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).

Similar idea to 3Sum, compare each sum with the target, if closer update the current min diff and set the result.

public int threeSumClosest(int[] num, int target) {
        if (num==null || num.length<3) {
            return -1;
        }
        //sort array first
        Arrays.sort(num);

        int result = 0;
        int finalDiff = Integer.MAX_VALUE;

        for (int i=0; i<num.length-2; i++) {
            int start = i+1;
            int end = num.length-1;

            while (start<end) {
                int sum = num[i] + num[start] + num[end];
                int diff = Math.abs(sum-target);
                if (diff<finalDiff) {
                    finalDiff = diff;
                    result = sum;
                }

                //move start if sum is less than target
                if (sum<=target) {
                    start=start+1;
                } else {
                    end=end-1;
                }            
            }


        }
        return result;
    }