Permutation

#include "stdafx.h"
#include <stdio.h>
#include <string.h>
#include <assert.h>

/*
 *        Swap two integer.
 * Param:
 *    a: One integer.
 *    b: Another integer.
 */
inline void swap(int &a, int &b)
{
    int c = a ;
    a = b ; 
    b = c ;
}

/*
 *        Print a line of numbers in 'arr'.
 * Param:
 *    arr: The array which contain a line of numbers.
 *    len: The number of elements in 'arr'.
 */
void p_line(int arr[], int len)
{
    for (int i = 0 ; i < len ;i++)
    {
        printf("%d ", arr[i]) ;
    }
    printf("\n") ;
}

/*
 *        The procedure of generating permutation.
 * Param:
 *    arr: The array containing numbers.
 *    len: The number of elements in 'arr'.
 *    from: This parameter identify the begining index where
 * to generate permutation.
 *    to: This parameter identify the ending index where to 
 * stop the procedure.
 * 
 * Note:
 *        This function will put the result to STDOUT.
 */
void permutation(int arr[], int len, int from, int to)
{
    if (from + 1 >= to)
    {
        p_line(arr, len) ;
    }
    else
    {
        for (int i = 0 ;i < to-from ;i++)
        {
            swap(arr[from], arr[from+i]) ;
            permutation(arr, len, from+1, to) ;
            swap(arr[from], arr[from+i]) ;
        }
    }
}

/*
 *        Generate permutation begin at 'from' and 
 * ending at 'to'.
 *        This function is a interface of function 
 * 'permutation'. 
 * 
 * Param:
 *    m: The begining number.
 *    n: The ending number.
 * 
 * Note:
 *        This function will put the result to STDOUT.
 */
void gen_permutation(int m, int n)
{
    assert(m <= n) ;

    int *arr = new int[n-m] ;
    memset(arr, '\0', (n-m) * sizeof(arr[0])) ;
    for (int i = 0 ;i < n-m ;i++)
    {
        arr[i] = m+i ;
    }

    permutation(arr, n-m, 0, n-m) ;

    delete []arr ;
    arr = NULL ;
}

int  main()
{
    gen_permutation(5, 10) ;
}