//-------------------------------------------------------------------
//	permlist.cpp
//
//	This program displays a list of all the permutations of the 
//	first  n  uppercase letters of the alphabet where the value
//	for  n  is supplied by the user as a command-line argument. 
//
//		to compile:  g++ permlist.cpp -o permlist
//		to execute:  ./permlist <n>
//
//	programmer: ALLAN CRUSE
//	written on: 01 MAY 2011
//-------------------------------------------------------------------

#include <stdio.h>	// for printf(), fprintf() 
#include <stdlib.h>	// for atoi(), exit() 

#define MAXSIZE 26	// number of uppercase letters

char list[ MAXSIZE ];	// array of uppercase letters
int	n = 3;		// order for the permutations

void permute( char list[], int k, int m )
{
	if ( k < m ) for (int i = k; i < m; i++)
			{
			// swap a[i] with a[m-1]
			char	temp = list[ i ];
			list[ i ] = list[ m-1 ];
			list[ m-1 ] = temp;
			
			permute( list, k, m-1 );

			// swap a[m-1] with a[i] 
			temp = list[ i ];
			list[ i ] = list[ m-1 ];
			list[ m-1 ] = temp;
			}
	else 	{ 
		for (int i = 0; i < n; i++) printf( "%c", list[ i ] );
		printf( "\n" );
		}		
}

int main(int argc, char **argv )
{
	// get command-line argument
	if ( argc > 1 ) n = atoi( argv[ 1 ] );
	if (( n < 1 )||( n > MAXSIZE )) 
		{ fprintf( stderr, "Invalid argument\n" ); exit(1); }

	// initialize the character-list
	for (int i = 0; i < MAXSIZE; i++) list[ i ] = (char)('A' + i);

	// use recursion to show all permulations on first n letters
	printf( "\n" ); permute( list, 0, n ); printf( "\n" );
}