3Sum

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.

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.

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

public class Solution {    public ArrayList<ArrayList<Integer>> threeSum(int[] num) {// Start typing your Java solution below// DO NOT write main() functionArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();if(num.length == 0)return res;ArrayList<Integer> inner;Arrays.sort(num);int origin, left, right, sum;for (int i = 0; i < num.length - 2; ) {//no need for i++ hereorigin = num[i];left = i + 1;right = num.length - 1;while (left < right) {sum = origin + num[left] + num[right];if (sum == 0) {inner = new ArrayList<Integer>();inner.add(origin);inner.add(num[left]);inner.add(num[right]);res.add(inner);int temp = num[left];while(left < right && temp == num[left])//skip same numberleft++;temp = num[right];while(left < right && temp == num[right])//skip same numberright--;} else if (sum > 0) {right--;} elseleft++;}            while(++i < num.length && num[i] == origin);//skip same origins}return res;}}