GCD.java

import java.util.*;

public class GCD{

    public static int gcd(int a, int b){
        if (b==0) return a;
        return gcd(b, a%b);
    };

    public static void main(String[] args){
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a number:");
        int x = scanner.nextInt();
        ArrayList< ArrayList<Integer> > grid = new ArrayList< ArrayList<Integer> >();
        ArrayList<Integer> answers = new ArrayList<Integer>();
        for (int i = 1; i <= x; i++){
            for (int j=1; j <=x; j++ ){
                ArrayList<Integer> inner = new ArrayList<Integer>();
                inner.add(i);
                inner.add(j);
                grid.add(inner);
            };
        };
        for (int i = 0; i < grid.size(); i++){
            answers.add(gcd(grid.get(i).get(0), grid.get(i).get(1)));
        }
        System.out.print("  ");
        for (int i=1; i<=x; i++){
            System.out.print(i);
            System.out.print(" ");
        }
        System.out.println();
        int w = 1;
        while(answers.size() != 0){ 
            System.out.print(w);
            System.out.print(" ");
            for (int j = 0; j < x; j++){
                System.out.print(answers.get(0));
                System.out.print(" ");
                answers.remove(0);
            }
            w++;
            System.out.println();
        }
        //System.out.println(answers);
    };
};