public List<List<Integer>> threeSum(int[] nums) {

Arrays.sort(nums);

List<List<Integer>> list = new ArrayList<>();

for (int i = 0; i < nums.length && nums[i] <= 0; i++) {

if (i == 0 || nums[i - 1] != nums[i]) {

twoSumHelper(nums, i, list);

}

}

return list;

}

private void twoSumHelper(int[] nums, int i, List<List<Integer>> list) {

int low = i + 1;

int high = nums.length - 1;

while (low < high) {

int sum = nums[i] + nums[low] + nums[high];

if (sum < 0 || (low > i + 1 && nums[low] == nums[low - 1])) {

low++;

}

else if (sum > 0 || (high < nums.length - 1 && nums[high] == nums[high + 1])) {

high--;

}

else {

list.add(Arrays.asList(nums[i], nums[low++], nums[high--]));

}

}

}