Interview Question 3Sum Closest

By Fatih KABAKCI

The problem is to find out the sum of three integers in an array which sum of them is closest to the target that is a given number. This problem is very similar to the problem #15 3Sum which asks the list of the sum of three integers in an array is zero. In that problem, the target is actually zero. However, this one could be any integer.

Problem #16 - 3Sum Closest

Description: 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.

Difficulty: Medium

Solution in Java

package com.fatihkabakci.Medium._3SumClosest;

import java.util.Arrays;

/**
 * 
 * @author fkabakci
 * 
 * Problem Description: 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:
 * 
 * 1. Sort the input array.
 * 2. Initialize closestSum as furthest of positive or negative side depending on sign of the target to make it farthest.
 * 3. Start with getting first, second and last element.
 * 4. Add up them.
 * 5. Update distances.
 * 	  Set current distance
 * 	  Set closest distance	
 * 6. If sum equals to target,
 * 		 then return it immediately.
 * 	  If sum is less than target,
 * 	     then close to greater one. (Skip to third one by increasing loop variable j)
 * 	  If sum is greater than target,
 * 		 then close to lesser one. (Skip to previous one of the last one by decreasing loop variable k)
 */

public class _3SumClosest {	
	public int threeSumClosest(int[] nums, int target) {
		if (nums.length < 3)
			return 0;
		Arrays.sort(nums);

		int closestSum = (target < 0 ) ? Integer.MIN_VALUE : Integer.MAX_VALUE;
		int i = 0, j, k;
		while (i < nums.length - 2) {
			j = i + 1;
			k = nums.length - 1;
			while (j < k) {
				int sum = nums[i] + nums[j] + nums[k];
				int distance = Math.abs(sum - target);
				int closestDistance = Math.abs(closestSum - target);
				if (distance < closestDistance) {
					closestSum = sum;
				}

				if (sum == target)
					return sum;
				else if (sum < target) {
					j++;
				} else
					k--;
			}
			i++;
		}
		return closestSum;
	}

	public static void main(String[] args) {
		_3SumClosest c = new _3SumClosest();
		System.out.println(c.threeSumClosest(new int[]{-3, -2, -5, 3, -4}, -1));
	}
}

Similar Problems

#15 3Sum

#18 4Sum