程序代码：

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

unsigned mask_next( unsigned mask[], unsigned val )
{
    size_t r;
    for( r=val; mask[r]==0; ++r );
    mask[r] = 0;
    return r;
}

bool next( size_t n, size_t m, unsigned a[] )
{
    for( size_t i=n-1-m; i!=0; --i, i-=(i!=0 && i%m==0) )
    {
        if( a[i] < a[i/m*m+2*m-1] )
        {
            size_t t = i/m*m+2*m-1;
            for( size_t j=i/m*m+m; j!=n; ++j )
                if( a[j]>a[i] && a[j]<a[t] )
                    t = j;

            unsigned tmp = a[i];
            a[i] = a[t];
            a[t] = tmp;

            if( i <  n-m-1 )
            {
                unsigned mask[n];
                memset( mask, 0, n*sizeof(mask[0]) );
                for( size_t j=i+1; j!=n; ++j )
                    mask[a[j]] = 1;

                for( size_t j=i+1; j!=i/m*m+m; ++j )
                    a[j] = mask_next( mask, a[i] );
                for( size_t j=i/m*m+m; j!=n; ++j )
                    a[j] = mask_next( mask, 0 );
            }
            return true;
        }
    }

    return false;
}

int main( void )
{
    const size_t n = 15;
    const size_t m = 3;

    unsigned cnt = 0;
    unsigned a[15] = { 0,1,2,3,4,5,6,7,8,9,10,11,12,13,14 };
    for( bool b=true; b; b=next(n,m,a) )
    {
        //for( size_t i=0; i!=n; ++i )
        //    printf( "%u%s", a[i], i+1==n?"\n":(", "+((i+1)%m!=0)) );

        ++cnt;
    }
    printf( "--- %u ---\n", cnt );

    return 0;
}