# 3Sum

## Problem

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.

## Example

For example, given array S = {-1 0 1 2 -1 -4}, A solution set is:

(-1, 0, 1)
(-1, -1, 2)

## Note

Elements in a triplet (a,b,c) must be in non-descending order. (ie, a ≤ b ≤ c)

The solution set must not contain duplicate triplets.

## Code - Java

public class Solution {
/**
* @param numbers : Give an array numbers of n integer
* @return : Find all unique triplets in the array which gives the sum of zero.
*/
public ArrayList<ArrayList<Integer>> threeSum(int[] nums) {
ArrayList<ArrayList<Integer>> result = new ArrayList<>();

Arrays.sort(nums);

for (int i = 0; i < nums.length - 2; i++) {
if (i > 0 && nums[i] == nums[i - 1]) continue;
int left = i + 1;
int right = nums.length - 1;

while (left < right) {
int sum = nums[i] + nums[left] + nums[right];
if (sum == 0) {
while(left < right && nums[left] == nums[left + 1]) left++;
while(left < right && nums[right] == nums[right - 1]) right--;
left++;
right--;
} else if (sum < 0) {
left++;
} else {
right--;
}
}
}
return result;
}
}