Example: 3 SUM - rFronteddu/general_wiki GitHub Wiki

Notice that the solution set must not contain duplicate triplets.
class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        List<List<Integer>> result = new LinkedList<>();
        
        Arrays.sort (nums);

        for (int i = 0; i < nums.length - 2; i++) {
            // skip duplicate elements for i
            if (i > 0 && nums[i] == nums[i - 1]) {
                continue;
            }
            int j = i + 1;
            int k = nums.length - 1;         

            while (j < k) {
                int sum = nums[i] + nums[j] + nums[k];
                if(sum == 0) {
                    result.add(Arrays.asList(nums[i], nums[j], nums[k]));
                    // skip duplicate elements for j
                    while (j < k && nums[j] == nums [j + 1]) {
                        j++;
                    }

                    // skip duplicate elements for k
                    while (j < k && nums[k] == nums [k - 1]) {
                        k--;
                    }

                    j++;
                    k--;
                } else if (sum < 0) {
                    j++;
                    // increase the sum
                } else {
                    k--;
                    // decrease the sum
                }
            }
        }
        return result;
    }
}