// polymult.java
//
//
// This program read an input n from the user.
// Then, it either reads or randomly generates 2 polynomials,
// 		each with n coefficients
// It multiplies these 2 polynomials.
// Finally, it prints out the result of the multiplication.
//
//
// A polynomial with n coefficient is represented as
// an array of n integers.
//
//
// The program contains the following subroutines:
//
// public static void polyread( int [] p, int n, BufferedReader br)
//											throws IOException
//    This function reads in n coefficients from the user for
//    polynomial p
//
// public static void polyrand( int [] p, int n)
//    This function creates random coefficients for polynomial p,
//    which has n coefficients.
//
// public static void polyprint( int [] p, int n)
//    This function prints the coefficients of the polynomial on the screen
//    starting with the coefficient of the monomial of degree 0.
//
// public static void polymult( int [] p, int [] q, int [] r, int n)
//    This function multiplies polynomials p and q, each has n coefficients
//    and stores the result in r.
//

import java.io.*;
import java.util.*;

public class polymult
{

	public static void main(String [] args) throws IOException
	{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

   		int [] a, b, c;
   		int n;

   		System.out.println("Enter N: ");
   		n = Integer.parseInt(br.readLine());

   		a=new int[n];
   		b=new int[n];
   		if (n <= 10)
   		{
   			polyread(a,n,br); // read the first polynomial
      		polyread(b,n,br); // read the second polynomial
   		}
   		else
   		{
   			polyrand(a,n); // random first polynomial
   			polyrand(b,n); // random second polynomial
   		}

   		c=new int[2*n-1];
   		polymult(a,b,c,n); // multiplying the polynomials

   		// printing out the result
   		System.out.println(" The coefficients of the first polynomial are");
   		polyprint(a,n);
   		System.out.println(" The coefficients of the second polynomial are");
   		polyprint(b,n);
   		System.out.println(" The coefficients of the resulting polynomial are");
   		polyprint(c,2*n-1);
	}

	public static void polyread( int [] p, int n, BufferedReader br)
											throws IOException
	{
		System.out.println("Please enter the " + n + " coefficients, sep. by spaces");
		StringTokenizer S = new StringTokenizer(br.readLine());
		for (int i = 0; i < n; i++)
		{
			p[i] = Integer.parseInt(S.nextToken());
		}
	}

	public static void polyrand( int [] p, int n)
	{
   		for( int i=0; i<n; i++) {
      		p[i] = ((int) (Math.random() * 41))-20;
		}
	}

	public static void polyprint( int [] p, int n)
	{
		for( int i=0; i<n; i++) {
			System.out.print(p[i] + " ");
		}
   		System.out.println();
	}

	public static void polymult( int [] p, int [] q, int [] r, int n)
	{

		for( int k=0; k<2*n-1; k++) {
      		r[k]=0;
		}
		for( int i=0; i<n; i++) {
			for( int j=0; j<n; j++) {
				r[i+j] += p[i]*q[j];
			}
		}
	}
}