程序代码：

#include <stdio.h>

int main()
{
    unsigned long octamer_count[65536] = { 0 };

    ////// 1 //////
    {
        FILE* file = fopen( "result22.txt", "rb" );
        if( !file )
        {
            puts( "cannot open the input file.");
            return 1;
        }
        {
            unsigned long octamer;
            unsigned long octamer_n = 0;
            char c;
            for( ; fread(&c,1,1,file)==1; )
            {
                switch( c )
                {
                    case 'A':
                        octamer = (octamer*4+0)%65536; ++octamer_n; break;
                    case 'T':
                        octamer = (octamer*4+1)%65536; ++octamer_n; break;
                    case 'C':
                        octamer = (octamer*4+2)%65536; ++octamer_n; break;
                    case 'G':
                        octamer = (octamer*4+3)%65536; ++octamer_n; break;
                    case '\r':
                    case '\n':
                        continue;
                    default:
                        puts( "Fuck" );
                    case 'N':
                        octamer_n = 0;
                        continue;
                }
                if( octamer_n < 8 )
                    continue;
                octamer_n = 8;

                ++octamer_count[octamer];
            }
        }
        fclose( file );
    }

    ////// 2 //////
    {
        FILE* fileout = fopen( "result22_ouput.txt", "wt" );
        if( !fileout )
        {
            puts( "cannot open the output file.");
            return 2;
        }
        {
            unsigned int i, j;
            for( i=0; i<sizeof(octamer_count)/sizeof(octamer_count[0]); ++i )
            {
                if( octamer_count[i] == 0 )
                    continue;
                for( j=65536/4; j!=0; j/=4 )
                    fprintf( fileout, "%c", "ATCG"[i/j%4] );
                fprintf( fileout, " %u\n", octamer_count[i] );
            }
        }
        fclose( fileout );
    }

    return 0;
}