LeetCode - 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.

public ArrayList<ArrayList<Integer>> threeSum(int[] num) { ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();   if (num.length < 3) return result;   // sort array Arrays.sort(num);   for (int i = 0; i < num.length - 2; i++) { // //avoid duplicate solutions if (i == 0 || num[i] > num[i - 1]) {   int negate = -num[i];   int start = i + 1; int end = num.length - 1;   while (start < end) { //case 1 if (num[start] + num[end] == negate) { ArrayList<Integer> temp = new ArrayList<Integer>(); temp.add(num[i]); temp.add(num[start]); temp.add(num[end]);   result.add(temp); start++; end--; //avoid duplicate solutions while (start < end && num[end] == num[end + 1]) end--;   while (start < end && num[start] == num[start - 1]) start++; //case 2 } else if (num[start] + num[end] < negate) { start++; //case 3 } else { end--; } }   } }   return result; }

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