class Permute
{
	// this is problem P9.13 from the textbook
	// it is similar (but more difficult than)
	// the phone number mapping quiz question.

	public static void permuteHelper( int[] prefix, int[] toPermute )
	{
		// this method must consider all orders of numbers
		// in "toPermute" and append them to "prefix".  it
		// does this recursively.
		if( toPermute.length == 0 ) {
			printArray( prefix );
		} else {
			int[] newPrefix  = new int[prefix.length+1];
			int[] newPermute = new int[toPermute.length-1];

			// copy from prefix to newPrefix
			for( int i=0; i < prefix.length; i++ ) {
				newPrefix[i] = prefix[i];
			}

			for( int i=0; i < toPermute.length; i++ ) {
				// try all elements in toPermute

				// add each one to newPrefix
				newPrefix[prefix.length] = toPermute[i];

				// copy all elements except toPermute[i]
				// into newPermute array
				int k=0;
				for( int j=0; j < toPermute.length; j++ ) { 
					if( j != i )
						newPermute[k++] = toPermute[j];
				}

				// call ourselves recursively
				permuteHelper( newPrefix, newPermute );
			}
		}
	}

	public static void permute( int n )
	{
		int[] prefix    = new int[0];
		int[] toPermute = new int[n];

		// initialize the array of values to permute
		for( int i=0; i<n; i++ )
			toPermute[i] = i;

		permuteHelper( prefix, toPermute );
	}

	// this method prints the contents of an array
	public static void printArray( int[] a )
	{
		for( int i=0; i < a.length; i++ ) {
			System.out.print( a[i] + " " );
		}
		System.out.println();  // go to next line
	}

	public static void main( String[] args )
	{
		permute( 4 );
	}
}