leetcode 15 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) {    ArrayList<ArrayList<Integer>>  list = new ArrayList<ArrayList<Integer>>();        Arrays.sort(num);        int n1,n2,n3;        for(n1=0;n1<num.length-2;n1++){        n2=n1+1;n3=num.length-1;while(n2<n3){if(num[n1]+num[n2]+num[n3]==0){ArrayList<Integer> tmpList = new ArrayList<Integer>();tmpList.add(num[n1]);tmpList.add(num[n2]);tmpList.add(num[n3]);list.add(tmpList);n2++;while(num[n2]==num[n2-1]&&n2<n3){n2++;}}else if(num[n1]+num[n2]+num[n3]>0){n3--;}else{n2++;}}        while(num[n1]==num[n1+1]&&(n1<(num.length-2))){        n1++;        }        }return list;    }}