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)

Code:

public class Solution {    public ArrayList<String> threeSum(int[] num) {        ArrayList<String> list = new ArrayList<String>();        HashSet<String> all = new HashSet<String>();        Arrays.sort(num);        for (int i = 0; i < num.length - 2; i++) {            int j = i + 1;            int z = num.length - 1;            while (j < z) {                if (num[i] + num[j] + num[z] == 0) {                    String str = num[i] + ", " + num[j] + ", " + num[z];                    all.add(str);                    j++;                    z--;                } else if (num[i] + num[j] + num[z] > 0) {                    z--;                } else {                    j++;                }                           }        }                for (String str : all) {            String[] items = str.split(" ");            ArrayList<String> triplet = new ArrayList<String>();            list.add(triplet);                    }        return list;    }}