class 3SumProblem {
    Map<Integer, HashSet<Integer>> entryIndexMap = new HashMap<>();
    public List<List<Integer>> threeSum(int[] nums) {
        Arrays.sort(nums);
        List<List<Integer>> sumList = new ArrayList<>();

        for (int i = 0; i < nums.length; i++) {
            int num = nums[i];
            HashSet<Integer> indices = entryIndexMap.get(num);
            if (indices != null) {
                indices.add(i);
            } else {
                indices = new HashSet<>();
                indices.add(i);
                entryIndexMap.put(num, indices);
            }
        }

        for (int i = 0; i < nums.length - 1; i++) {
        // We are skipping the parts where there is repeated continuous values of i and j. Because these are going to lead to repeated solution
            if (!(i > 0 && nums[i] == nums[i - 1])) {
                for (int j = i + 1; j < nums.length; j++) {
                    if (!(j > i + 1 && nums[j] == nums[j - 1])) {
                        int sum = nums[i] + nums[j];
                        int remaining = 0 - sum;
                        if (entryIndexMap.get(remaining) != null) {
                            Set<Integer> indices = entryIndexMap.get(remaining);
                            for (int index : indices) {
                                if (index > i && index > j) {
                                    List<Integer> list = new ArrayList<>();
                                    list.add(nums[i]);
                                    list.add(nums[j]);
                                    list.add(nums[index]);
                                    sumList.add(list);
                                    break;
                                }
                            }
                        }
                    }
                }
            }
        }
        return sumList;
    }
}