threeSum.java

import java.util.*;

class Solution {
    public List<List<Integer>> threeSum(int[] nums) {
        if (nums.length < 3){
          return new ArrayList<>();
        }
        
        Set<List<Integer>> result = new HashSet<>();
        Arrays.sort(nums);
        for (int i = 0; i < nums.length - 2; i++){
          int j = i+1;
          int k =nums.length - 1;
          
          while(j<k){
            int sum = nums[i] + nums[j] + nums[k];
            List <Integer> list = new ArrayList<>();
            if (sum == 0){
              list.add(nums[i]);
              list.add(nums[j]);
              list.add(nums[k]);
              j++;
              k--;
              result.add(list);
            } else if (sum > 0){
              k--;
            } else {
              j++;
            }
          }
        }
        return new ArrayList<List<Integer>>(result);
    }
    
    
    public static void main (String[] args){
        Solution solution = new Solution();
        
        int[] nums = {-1,0,1,2,-1,-4};
        List<List<Integer>> result = solution.threeSum(nums);
        
        System.out.println(result);
    }
}