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).

Our approach:

We just select the all the possible combinations of two elements and use a variation of binary search that looks for the closest element instead of the exact one.

public class Solution {

    public int threeSumClosest(int[] num, int target) 

    {

        int error = Integer.MAX_VALUE;

        int solution = 0;

        if(num.length<3)

            return solution;

        Arrays.sort(num);

        for(int i=0; i<num.length-2; i++)

        {

            for(int j=i+1; j<num.length-1;j++)

            {

                int temp = findSumClosest(num, target, num[i]+num[j], j+1) + num[i] + num[j];

                if(error>Math.abs(target-temp))

                {

                    solution = temp;

                    error = Math.abs(target-temp);

                }

            }

        }

        return solution;

    }

    

    private int findSumClosest(int[] num, int target, int tempSum, int start)

    {

        int goal = target-tempSum;

        int p1 = start;

        int p2 = num.length-1;

        while(p1<p2)

        {

            int middle = (p1+p2)/2;

            if(Math.abs(num[middle]-goal)>Math.abs(num[middle+1]-goal))

                p1=middle+1;

            else

                p2=middle;

        }

        return num[p1];

    }

}