TwoSumProblem.java

package Misc;

import java.util.*;
import java.util.stream.Collectors;

public class TwoSumProblem {
	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();
		}
		TwoSumProblem t = new TwoSumProblem();
		System.out.println("Brute Force Approach\n"+Arrays.toString(t.BruteForce(arr,ts))+"\n");
		System.out.println("Two Pointer Approach\n"+Arrays.toString(t.TwoPointer(arr,ts))+"\n");
		System.out.println("Hashmap Approach\n"+Arrays.toString(t.HashMap(arr,ts)));
		
	}
public int[] BruteForce(int[] nums, int target) {
	     //Brute Force Approach 
	        int ans[]=new int[2];
	        for (int i=0;i<nums.length;i++)
	        {
	            for (int j=i+1;j<nums.length;j++)
	            {
	                if(nums[i]+nums[j]==target)
	                {
	                    ans[0]=i;
	                    ans[1]=j;
	                   
	                    break;
	                }
	                    
	            }
	        }
	        
	        return ans;
	 }


public int[] TwoPointer(int[] nums, int target) {		 
		 // HashMap Approach
		 int ans[]=new int[2];
		 HashMap<Integer,Integer> hm=new HashMap<Integer,Integer>();    
	        for(int i =0;i<nums.length;i++)
	        {
	            hm.put(i,nums[i]);
	        }
	        HashMap<Integer, Integer> temp
	            = hm.entrySet()
	                  .stream()
	                  .sorted((i1, i2)
	                              -> i1.getValue().compareTo(
	                                  i2.getValue()))
	                  .collect(Collectors.toMap(
	                      Map.Entry::getKey,
	                      Map.Entry::getValue,
	                      (e1, e2) -> e1, LinkedHashMap::new));
	         
	        int start = 0;
	        int end = nums.length - 1;
	        while (start<end)
	        {   int currSum=(Integer) temp.values().toArray()[start]+(Integer) temp.values().toArray()[end];
	         
	            if(currSum==target)
	            {   
	                ans[0]=(Integer) temp.keySet().toArray()[start];
	                ans[1]=(Integer) temp.keySet().toArray()[end];
	                break;
	            }
	            else if(currSum>target)
	                end-=1;
	            else if(currSum<target)
	            {
	                start+=1;
	            }
	            
	        }
		 return ans;
	        
}


public int[] HashMap(int[] nums, int target) {	
	 //Using Hashmaps
     int ans[]=new int[2];
     HashMap<Integer,Integer> hm=new HashMap<Integer,Integer>();    
     for(int i=0;i<nums.length;i++)
     {
         hm.put(nums[i],i);
     }
     for(int i =0;i<nums.length;i++)
     {
         int t = target - nums[i];
         if(hm.containsKey(t) && hm.get(t)!=i)
         {
             ans[0]=i;
             ans[1]=hm.get(t);
             break;
         }
     }
     
     return ans;
 }

}