## 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).

## Explanation

3Sum Closest is a follow-up question for two sum.

For 3Sum Closest, we are going to find the closet sum to the target. The closet sum could be the target itself or a number close to the target.

- First, we can sort the array into ascending order.
- Second, we declare an integer variable called closetSum. That’s the final value we are going to return.
- Then we can iterate all the numbers in the array. Whenever visiting a number, we should find two numbers in the rest of array which adds the number closet to target. Once iteration finished, we get the result.

## Video Tutorial

## Java Solution

class Solution { public int threeSumClosest(int[] nums, int target) { if (nums == null || nums.length < 3) { return -1; } Arrays.sort(nums); int closetSum = nums[0] + nums[1] + nums[2]; for (int i = 0; i < nums.length; i++) { int left = i + 1; int right = nums.length - 1; while (left < right) { int sum = nums[i] + nums[left] + nums[right]; if (Math.abs(sum - target) < Math.abs(closetSum - target)) { closetSum = sum; } if (sum < target) { left++; } else { right--; } } } return closetSum; } }