3 Sum Closest

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 class Solution {
    public int threeSumClosest(int[] num, int target) {
        // Start typing your Java solution below
        // DO NOT write main() function
        Arrays.sort(num);
        ArrayList> list = new ArrayList>();
        
        Integer closest = null;
        
        for (int i = 0; i <= num.length - 3; i++) {
            int a = num[i];
            int j = i+1;
            int k = num.length - 1;
            if (closest == null) closest = a + num[j] + num[k];
            
            int best = closest.intValue();
            
            while (j < k) {
                int b = num[j];
                int c = num[k];
                if (a + b + c == target) {
                    return a + b + c;
                }
                else if (a + b + c < target) {
                    if (Math.abs(a + b + c - target)
                        < Math.abs(best - target)) {
                        best = a + b + c;
                    }
                    j++;
                }
                else {
                    if (Math.abs(a + b + c - target)
                        < Math.abs(best - target)) {
                        best = a + b + c;
                    }
                    k--;
                }
            }
            
            if (Math.abs(best - target) < Math.abs(closest.intValue() - target)) {
                closest = best;
            }
        }
        
        return closest.intValue();
    }
    
}