Write a method called writeSequence that accepts an integer n as a parameter and

Question

Write a method called writeSequence that accepts an integer n as a parameter and prints to the
console a symmetric sequence of n numbers composed of descending integers that ends in 1, followed
by a sequence of ascending integers that begins with 1. The following table indicates the output that
should be produced for various values of n:

Method call Output produced
-----------------------------------------
writeSequence(1); 1
writeSequence(2); 1 1
writeSequence(3); 2 1 2
writeSequence(4); 2 1 1 2
writeSequence(5); 3 2 1 2 3
writeSequence(6); 3 2 1 1 2 3
writeSequence(7); 4 3 2 1 2 3 4
writeSequence(8); 4 3 2 1 1 2 3 4
writeSequence(9); 5 4 3 2 1 2 3 4 5
writeSequence(10); 5 4 3 2 1 1 2 3 4 5

Notice that when n is odd the sequence has a single 1 in the middle, whereas for even values it has two
1s in the middle. Your method should throw an IllegalArgumentException if it is passed a value less
than 1. Write a main program to test 1, 5, 6, 9 and 10.

Explanation / Answer

public class NumberSequence
{
   public static void main(String[] args)
   {
       writeSequence(1);
       System.out.println();
       writeSequence(5);
       System.out.println();
       writeSequence(6);
       System.out.println();
       writeSequence(9);
       System.out.println();
       writeSequence(10);
       System.out.println();
       writeSequence(-9);
       System.out.println();
   }
  
   public static void writeSequence(int num)
   {
       if (num < 0)
           throw new IllegalArgumentException("Error: score is negative.");
       else
       {
           if(num%2==0)
           {
               for(int i=num/2; i>=1; i--)
                   System.out.print(i + " ");
               for(int i=1; i<=(num/2); i++)
                   System.out.print(i + " ");
           }
           else
           {
               for(int i=(num+1)/2; i>0; i--)
                   System.out.print(i + " ");
               for(int i=2; i<=((num+1)/2); i++)
                   System.out.print(i + " ");
           }          
       }      
   }
}

Output:

1
3 2 1 2 3
3 2 1 1 2 3
5 4 3 2 1 2 3 4 5
5 4 3 2 1 1 2 3 4 5

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