ThreeSumProblem.java

import java.util.*;
public class ThreeSumProblem {
	public static void main(String args[])
	{
		Scanner scan = new Scanner(System.in);
		System.out.print("Enter the target sum ");
		int ts= scan.nextInt();
		System.out.print("Enter the number of elements in the array ");
		int n = scan.nextInt();
		System.out.println("Enter all your array elements:");
		int arr[]= new int[n];
		for(int i=0;i<n;i++)
		{ 
			arr[i]=scan.nextInt();
		}
		ThreeSumProblem th = new ThreeSumProblem();
		System.out.println("Brute Force Approach\n"+(th.BruteForce(arr,ts))+"\n");
		System.out.println("Two Pointer Approach\n"+(th.TwoPointer(arr,ts))+"\n");
		System.out.println("Hashmap Approach\n"+(th.Hashmap(arr,ts)));

}
	public List<List<Integer>> BruteForce(int[] nums,int target) {
        List<List<Integer>> arr = new ArrayList<List<Integer>>();
       
        for(int i=0;i<nums.length;i++)
        {
             for(int j=i+1;j<nums.length;j++)
             {
                  for(int k=j+1;k<nums.length;k++)
                  {
                         if(nums[i]+nums[j]+nums[k]==target)
                         {  List<Integer> temp = new ArrayList<>();
                            temp.add(nums[i]);
                            temp.add(nums[j]);
                            temp.add(nums[k]);
                            Collections.sort(temp);
                            arr.add(temp);
                         }
                                 
                             
                      }
                  }
             }
        arr = new ArrayList<List<Integer>>(new LinkedHashSet<List<Integer>>(arr));
        return arr;
        }
	public List<List<Integer>> TwoPointer(int[] nums, int target) {
		 Arrays.sort(nums);
	        List<List<Integer>> arr = new ArrayList<List<Integer>>();
	        int start=0;
	        int end=0;
	        int i = 0;
	        while(i<nums.length-1)
	        {
	            start=i+1;
	            end=nums.length-1;
	            while (start<end)
	            {
	                if (nums[start]+nums[end]+nums[i]==target)
	                {
	                    List<Integer> temp = new ArrayList<>();
	                            temp.add(nums[i]);
	                            temp.add(nums[start]);
	                            temp.add(nums[end]);
	                            arr.add(temp);
	                            start++;
	                            end--;
	                }
	                else if (nums[start]+nums[end]+nums[i]<target)
	                    start+=1;
	                else
	                    end-=1;
	                    
	            }
	            i++;
	        }
	        Set<List<Integer>> set = new LinkedHashSet<List<Integer>>(arr);
			return new ArrayList<List<Integer>>(set);
	}
	public List<List<Integer>> Hashmap(int[] nums, int target) {
		 Arrays.sort(nums);
	        Set<List<Integer>> ts = new HashSet();
	        HashMap<Integer,Integer> hm = new HashMap<>();
	        
	        for(int i=0;i<nums.length;i++)
	        {
	            hm.put(nums[i],i);
	        }
	        
	        for(int i=0;i<nums.length;i++)
	        {
	            for(int j=i+1;j<nums.length;j++)
	            {
	                int t= target - nums[i] - nums[j];
	                if(hm.containsKey(t) && hm.get(t)>j)
	                {
	                     List<Integer> temp = new ArrayList<>();
		                            temp.add(nums[i]);
		                            temp.add(nums[j]);
		                            temp.add(t);
		                            ts.add(temp);
	                }
	            }
	        }
	        return new ArrayList(ts);
	}
	
}