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.

  1. For example, given array S = {-1 2 1 -4}, and target = 1.
  3. The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Solution:

  1. public class Solution {
  2.     public int threeSumClosest(int[] num, int target) {
  3.         Arrays.sort(num);
  5.         int n = num.length;
  6.         int closest = num[0] + num[1] + num[2];
  8.         for (int i = 0; i < n - 2; i++) {
  9.             int j = i + 1;
  10.             int k = n - 1;
  12.             while (j < k) {
  13.                 int sum = num[i] + num[j] + num[k];
  15.                 if (sum == target) {
  16.                     return sum;
  17.                 } else if (sum < target) {
  18.                     j++;
  19.                 } else {
  20.                     k--;
  21.                 }
  23.                 if (Math.abs(target - sum) < Math.abs(target - closest)) {
  24.                     closest = sum;
  25.                 }
  26.             }
  27.         }
  29.         return closest;
  30.     }
  31. }

Time complexity: O(n^2)