Find all unique triplets that sum to zero

Find all unique triplets that sum to zero

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

For example, given set S = {-1 0 1 2 -1 -4},

One possible solution set is:
(-1, 0, 1)
(-1, 2, -1)

Note that (0, 1, -1) is not part of the solution above, because (0, 1, -1) is the duplicate of (-1, 0, 1). Same with (-1, -1, 2).

For a set S, there is probably no “the” solution, another solution could be:
(0, 1, -1)
(2, -1, -1)

Solution:

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set<arrayList<int> > findTriplets(int[] a) {   // Sort the array   a = sort(a);    int[3] triplet;   set<triplet> triplets;   int n = a.length();   for (int i = 0;i < n-2; i++) {     int j = i + 1;     int k = n - 1;     while (j < k) {       int sum_two = arr[i] + arr[j];       if (sum_two + arr[k] < 0) {         j++;       } else if (sum_two + arr[k] > 0) {         k--;       } else {         triplet[0] = arr[i];         triplet[1] = arr[j];         triplet[2] = arr[k];         triplets.insert(triplet);         j++;         k--;       }     }   }   return triplets; }

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