Given an array of distinct elements. The task is to find triplets in array whose sum is zero.

findTriplets.java

import java.util.*;
public class findTriplets{

     public static void main(String []args){
        int[] input = {1, -2, -1, 0, 2};
        int result_n3 = findTriplets_n3(input);
        int result_n2 = findTriplets_n2(input);
        System.out.println(result_n3);
        System.out.println(result_n2);
     }
     
     public static int findTriplets_n3(int[] input){
         int count = 0;
         for(int i=0; i<input.length-2; i++)
            for(int j=i+1; j<input.length-1; j++)
                for(int k=j+1; k<input.length; k++)
                    if(input[i]+input[j]+input[k] == 0){
                        count++;
                        System.out.println(input[i]+" "+input[j]+" "+input[k]);
                    }
        return count;
     }
     
     public static int findTriplets_n2(int[] input){
         HashMap<Integer, Integer> pairs = new HashMap<Integer, Integer>();
         for(int i=0; i<input.length-1; i++)
            for(int j=i+1; j<input.length; j++)
                if(pairs.containsKey(input[i]+input[j]))
                    pairs.put(input[i]+input[j], (int) pairs.get(input[i]+input[j])+1);
                else{
                    pairs.put(input[i]+input[j], 1);
                    
                }

        int count = 0;
        for(int i=0; i<input.length; i++){
            if(pairs.containsKey(-1*input[i]))
                count += (int) pairs.get(-input[i]);
        }
        return count/3;
     }
}