TwoSum Solution

TwoSum.java

import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;

public class Main
{
    //O(n)
    public static String twoSum(List numbers, int target){
        Integer head = 0, 
                tail = numbers.size()-1,
                sum = 0;
                
        while(head < tail){
            sum = (int) numbers.get(head) + (int) numbers.get(tail);
            if(sum == target)
                return String.format("%s# element + %s# element = %s + %s = %s",
                            head+1,
                            tail+1,
                            (int) numbers.get(head), 
                            (int) numbers.get(tail),
                            target);
            
            if(sum > target)
                tail-=1;
            else
                head+=1;
        }
        return null;
    }
    
	public static void main(String[] args) {
	    Integer[] a = new Integer[] {1,1,1,2,2,3,4,5,5,6,7,9,9};
	    List<Integer> numbers = Arrays.asList(a);
	    System.out.println(twoSum(numbers,9));
	    
	}
}