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      1 /*
      2 Redistribution and use in source and binary forms, with or without
      3 modification, are permitted provided that the following conditions are met:
      4 
      5     * Redistributions of source code must retain the above copyright
      6     notice, this list of conditions and the following disclaimer.
      7 
      8     * Redistributions in binary form must reproduce the above copyright
      9     notice, this list of conditions and the following disclaimer in the
     10     documentation and/or other materials provided with the distribution.
     11 
     12     * Neither the name of "The Computer Language Benchmarks Game" nor the
     13     name of "The Computer Language Shootout Benchmarks" nor the names of
     14     its contributors may be used to endorse or promote products derived
     15     from this software without specific prior written permission.
     16 
     17 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
     18 AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     19 IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     20 ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
     21 LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     22 CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     23 SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     24 INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     25 CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     26 ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     27 POSSIBILITY OF SUCH DAMAGE.
     28 */
     29 
     30 /*
     31  * The Computer Language Shootout
     32  * http://shootout.alioth.debian.org/
     33  * Contributed by Heiner Marxen
     34  *
     35  * "fannkuch"	for C gcc
     36  *
     37  * $Id: fannkuch.1.gcc.code,v 1.15 2009-04-28 15:39:31 igouy-guest Exp $
     38  */
     39 
     40 #include <stdio.h>
     41 #include <stdlib.h>
     42 
     43 #define Int	int
     44 #define Aint	int
     45 
     46     static long
     47 fannkuch( int n )
     48 {
     49     Aint*	perm;
     50     Aint*	perm1;
     51     Aint*	count;
     52     long	flips;
     53     long	flipsMax;
     54     Int		r;
     55     Int		i;
     56     Int		k;
     57     Int		didpr;
     58     const Int	n1	= n - 1;
     59 
     60     if( n < 1 ) return 0;
     61 
     62     perm  = calloc(n, sizeof(*perm ));
     63     perm1 = calloc(n, sizeof(*perm1));
     64     count = calloc(n, sizeof(*count));
     65 
     66     for( i=0 ; i<n ; ++i ) perm1[i] = i;	/* initial (trivial) permu */
     67 
     68     r = n; didpr = 0; flipsMax = 0;
     69     for(;;) {
     70 	if( didpr < 30 ) {
     71 	    for( i=0 ; i<n ; ++i ) printf("%d", (int)(1+perm1[i]));
     72 	    printf("\n");
     73 	    ++didpr;
     74 	}
     75 	for( ; r!=1 ; --r ) {
     76 	    count[r-1] = r;
     77 	}
     78 
     79 #define XCH(x,y)	{ Aint t_mp; t_mp=(x); (x)=(y); (y)=t_mp; }
     80 
     81 	if( ! (perm1[0]==0 || perm1[n1]==n1) ) {
     82 	    flips = 0;
     83 	    for( i=1 ; i<n ; ++i ) {	/* perm = perm1 */
     84 		perm[i] = perm1[i];
     85 	    }
     86 	    k = perm1[0];		/* cache perm[0] in k */
     87 	    do {			/* k!=0 ==> k>0 */
     88 		Int	j;
     89 		for( i=1, j=k-1 ; i<j ; ++i, --j ) {
     90 		    XCH(perm[i], perm[j])
     91 		}
     92 		++flips;
     93 		/*
     94 		 * Now exchange k (caching perm[0]) and perm[k]... with care!
     95 		 * XCH(k, perm[k]) does NOT work!
     96 		 */
     97 		j=perm[k]; perm[k]=k ; k=j;
     98 	    }while( k );
     99 	    if( flipsMax < flips ) {
    100 		flipsMax = flips;
    101 	    }
    102 	}
    103 
    104 	for(;;) {
    105 	    if( r == n ) {
    106 		return flipsMax;
    107 	    }
    108 	    /* rotate down perm[0..r] by one */
    109 	    {
    110 		Int	perm0 = perm1[0];
    111 		i = 0;
    112 		while( i < r ) {
    113 		    k = i+1;
    114 		    perm1[i] = perm1[k];
    115 		    i = k;
    116 		}
    117 		perm1[r] = perm0;
    118 	    }
    119 	    if( (count[r] -= 1) > 0 ) {
    120 		break;
    121 	    }
    122 	    ++r;
    123 	}
    124     }
    125 }
    126 
    127     int
    128 main( int argc, char* argv[] )
    129 {
    130     int		n = (argc>1) ? atoi(argv[1]) : 0;
    131 
    132     printf("Pfannkuchen(%d) = %ld\n", n, fannkuch(n));
    133     return 0;
    134 }
    135