Worst Abuse of the C Preprocessor

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#ifndef  pdbq

#ifndef  n

#define  n 05

#endif   pqbd

#define  dpqb __FILE__ 

#define  ppbd "Move disk %d from peg %d to peg %d\n"

#define  pdbq

#if      n&01

#define  dqbp

#endif   bpdq

#if      n&02

#define  dbpq

#endif   pbdq

#if      n&04

#define  pbqd

#endif   qbpb

#if      n>>3

#define  bqdp

#endif   pbbq

main(){  pdbq

printf(  pdbq

#include dpqb

#define  qbdp

#include dpqb

);}      qbdp

#else    dpdp

#ifdef   dqbp

#define  bdpq

#endif   bpdd

#ifdef   dbpq

#define  bdpq

#endif   pqpb

#ifdef   pbqd

#define  bdpq

#endif   pdpp

#ifdef   bqdp

#define  bdpq

#endif   pdpp

#ifdef   bdpq

#undef   bdpq

#ifndef  dqbp

#define  dqbp

#ifndef  dbpq

#define  dbpq

#ifndef  pbqd

#define  pbqd

#ifndef  bqdp

#define  bqdp

#else    dbqb

#undef   bqdp

#endif   qdqb

#else    pdbq

#undef   pbqd

#endif   qdbp

#else    pqbb

#undef   dbpq

#endif   pqbd

#else    bbpp

#undef   dqbp

#endif   ppqb

#include dpqb

#ifndef  dqbp

#ifndef  dbpq

#ifndef  pbqd

#ifndef  bqdp

#define  bdpq

#endif   pbpp

#endif   qpdp

#endif   ddpb

#endif   qppb

#ifdef   bdpq

#undef   bdpq

#ifndef  qbdp

pdbq     ppbd

#else    qbbd

#ifdef   pqdb

,1,2,3   pqdb

#undef   pqdb

#define  qdbp

#else    bdbb

#ifdef   qdbp

,1,3,1   qdbp

#undef   qdbp

#else    bdbd

,1,1,2   pdbq

#define  pqdb

#endif   qppq

#endif   pqpb

#endif   bpdd

#else    pqpq

#ifndef  qbdp

pdbq     ppbd

#else    qqqb

,1       pdbq

#ifdef   dqbp

+1       dqbp

#endif   qqdb

#ifdef   dbpq

+2       dbpq

#endif   ppqb

#ifdef   pbqd

+4       pbqd

#endif   pqpp

#ifdef   bqdp

+8       bqdp

#endif   bbpb

#ifdef   pqdb

#ifdef   dqbp

,1,3     dqbp

#else    pddp

,3,1     pdbq

#endif   qpqq

#else    dbqb

#ifdef   qdbp

#ifdef   dqbp

,2,1     dqbp

#else    pqdb

,1,2     pdbq

#endif   dbdp

#else    pdpp

#ifdef   dqbp

,3,2     dqbp

#else    pdbb

,2,3     pdbq

#endif   pqpp

#endif   qbdp

#endif   pqpp

#endif   pdbp

#endif   pqdp

#include dpqb

#ifdef   dqbp

#undef   dqbp

#ifdef   dbpq

#undef   dbpq

#ifdef   pbqd

#undef   pbqd

#ifdef   bqdp

#undef   bqdp

#else    qddb

#define  bqdp

#endif   ppqp

#else    bddq

#define  pbqd

#endif   ddbq

#else    bbdb

#define  dbpq

#endif   qqbd

#else    ddbq

#define  dqbp

#endif   qbdb

#endif   qbdb

#endif   qbpp

引用元：https://www.ioccc.org/1995/vanschnitz.c

審査員・作者による説明：https://github.com/ioccc-src/winner/blob/main/1995/vanschnitz.hint

動作

ハノイの塔の解を表示する。デフォルトではディスク5枚。

$ gcc vanschnitz.c -o vanschnitz

$ ./vanschnitz
Move disk 1 from peg 1 to peg 2
Move disk 2 from peg 1 to peg 3
Move disk 1 from peg 2 to peg 3
Move disk 3 from peg 1 to peg 2
Move disk 1 from peg 3 to peg 1
Move disk 2 from peg 3 to peg 2
Move disk 1 from peg 1 to peg 2
Move disk 4 from peg 1 to peg 3
Move disk 1 from peg 2 to peg 3
Move disk 2 from peg 2 to peg 1
Move disk 1 from peg 3 to peg 1
Move disk 3 from peg 2 to peg 3
Move disk 1 from peg 1 to peg 2
Move disk 2 from peg 1 to peg 3
Move disk 1 from peg 2 to peg 3
Move disk 5 from peg 1 to peg 2
Move disk 1 from peg 3 to peg 1
Move disk 2 from peg 3 to peg 2
Move disk 1 from peg 1 to peg 2
Move disk 3 from peg 3 to peg 1
Move disk 1 from peg 2 to peg 3
Move disk 2 from peg 2 to peg 1
Move disk 1 from peg 3 to peg 1
Move disk 4 from peg 3 to peg 2
Move disk 1 from peg 1 to peg 2
Move disk 2 from peg 1 to peg 3
Move disk 1 from peg 2 to peg 3
Move disk 3 from peg 1 to peg 2
Move disk 1 from peg 3 to peg 1
Move disk 2 from peg 3 to peg 2
Move disk 1 from peg 1 to peg 2

ディスクの枚数はコンパイル時に指定できる。

$ gcc vanschnitz.c -o vanschnitz -Dn=3

$ ./vanschnitz
Move disk 1 from peg 1 to peg 2
Move disk 2 from peg 1 to peg 3
Move disk 1 from peg 2 to peg 3
Move disk 3 from peg 1 to peg 2
Move disk 1 from peg 3 to peg 1
Move disk 2 from peg 3 to peg 2
Move disk 1 from peg 1 to peg 2

解説

Cプリプロセッサによってハノイの塔を解いている。

#include __FILE__によって再帰することでループを行い、最終的にprintfを1つ呼び出すだけのmain関数になる。 例えばディスク3枚の設定（-Dn=3）でプリプロセスをした結果を整形したらこうなる。

main(){
  printf(
    "Move disk %d from peg %d to peg %d\n"
    "Move disk %d from peg %d to peg %d\n"
    "Move disk %d from peg %d to peg %d\n"
    "Move disk %d from peg %d to peg %d\n"
    "Move disk %d from peg %d to peg %d\n"
    "Move disk %d from peg %d to peg %d\n"
    "Move disk %d from peg %d to peg %d\n"
    ,1,1,2
    ,1
    +1
    ,1,3
    ,1,2,3
    ,1
    +2
    ,1,2
    ,1,3,1
    ,1
    +1
    ,3,2
    ,1,1,2
  );
}

このとおり、ハノイの塔の解自体はプリプロセス時にすべて特定してしまうので、プリプロセッサで解いていると言える。

コードはとてもいい感じに整形されている。 大体マクロ定義文ばかりで、定義はほぼ4文字。 識別子はb、d、p、qを組み合わせた4文字ばかりで非常に読みにくい。