The difference between two similar 3Sum algorithms?

I found a 3Sum problem at http://www.leetcode.com/onlinejudge that looks like this:

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 an array that gives the sum of zero.

Note: Elements in the triplet (a, b, c) must be in descending order. (i.e. 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)

I went through the site and found this proposed solution:

public ArrayList<ArrayList<Integer>> threeSum(int[] num) {
    Arrays.sort(num);
    HashSet<ArrayList<Integer>> lstSoln = new HashSet<ArrayList<Integer>>();

    ArrayList<Integer> tempArr = null;
    for (int i = 0; i < num.length; i++) {
        int j = i + 1;
        int k = num.length - 1;
        while (j < k) {
            int sum3 = num[i] + num[j] + num[k];
            if (sum3 < 0) {
                j++;
            } else if (sum3 > 0) {
                k--;
            } else {
                tempArr = new ArrayList<Integer>();
                Collections.addAll(tempArr, num[i], num[j], num[k]);
                lstSoln.add(tempArr);
                j++;
                k--;
            }
        }
    }

    return new ArrayList<ArrayList<Integer>>(lstSoln);
}

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if (num[i] > 0)
    break;

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