ThreeSum.java

import java.util.*;

public class ThreeSum {

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

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

        Arrays.sort(nums);

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

            int left = i + 1;
            int right = nums.length - 1;

            while (left < right) {
                int sum = nums[i] + nums[left] + nums[right];
                if (sum == 0) {
                    List<Integer> temp = new ArrayList<>();

                    temp.add(nums[i]);
                    temp.add(nums[left]);
                    temp.add(nums[right]);

                    ans.add(temp);

                    while (left < right && nums[left] == nums[left + 1]) {
                        left++;
                    }
                    while (left < right && nums[right] == nums[right - 1]) {
                        right--;
                    }
                    left++;
                    right--;
                } else if (sum < 0) {
                    left++;
                } else {
                    right--;
                }
            }
        }
        return ans;
    }

    public static void main(String[] args) {
        // Scanner ui = new Scanner(System.in);

        int nums[] = { -1, 0, 1, 2, -1, -4 };

        List<List<Integer>> result = threeSum(nums);
        System.out.println(result);

    }
}