tests2/30_hanoi.c

   1 /* example from http://barnyard.syr.edu/quickies/hanoi.c */
   2
   3 /* hanoi.c: solves the tower of hanoi problem. (Programming exercise.) */
   4 /* By Terry R. McConnell (12/2/97) */
   5 /* Compile: cc -o hanoi hanoi.c */
   6
   7 /* This program does no error checking. But then, if it's right,
   8    it's right ... right ? */
   9
  10
  11 /* The original towers of hanoi problem seems to have been originally posed
  12    by one M. Claus in 1883. There is a popular legend that goes along with
  13    it that has been often repeated and paraphrased. It goes something like this:
  14    In the great temple at Benares there are 3 golden spikes. On one of them,
  15    God placed 64 disks increasing in size from bottom to top, at the beginning
  16    of time. Since then, and to this day, the priest on duty constantly transfers
  17    disks, one at a time, in such a way that no larger disk is ever put on top
  18    of a smaller one. When the disks have been transferred entirely to another
  19    spike the Universe will come to an end in a large thunderclap.
  20
  21    This paraphrases the original legend due to DeParville, La Nature, Paris 1884,
  22    Part I, 285-286. For this and further information see: Mathematical
  23    Recreations & Essays, W.W. Rouse Ball, MacMillan, NewYork, 11th Ed. 1967,
  24    303-305.
  25  *
  26  *
  27  */
  28
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31
  32 #define TRUE 1
  33 #define FALSE 0
  34
  35 /* This is the number of "disks" on tower A initially. Taken to be 64 in the
  36  * legend. The number of moves required, in general, is 2^N - 1. For N = 64,
  37  * this is 18,446,744,073,709,551,615 */
  38 #define N 4
  39
  40 /* These are the three towers. For example if the state of A is 0,1,3,4, that
  41  * means that there are three discs on A of sizes 1, 3, and 4. (Think of right
  42  * as being the "down" direction.) */
  43 int A[N], B[N], C[N];
  44
  45 void Hanoi(int,int*,int*,int*);
  46
  47 /* Print the current configuration of A, B, and C to the screen */
  48 void PrintAll()
  49 {
  50    int i;
  51
  52    printf("A: ");
  53    for(i=0;i<N;i++)printf(" %d ",A[i]);
  54    printf("\n");
  55
  56    printf("B: ");
  57    for(i=0;i<N;i++)printf(" %d ",B[i]);
  58    printf("\n");
  59
  60    printf("C: ");
  61    for(i=0;i<N;i++)printf(" %d ",C[i]);
  62    printf("\n");
  63    printf("------------------------------------------\n");
  64    return;
  65 }
  66
  67 /* Move the leftmost nonzero element of source to dest, leave behind 0. */
  68 /* Returns the value moved (not used.) */
  69 int Move(int *source, int *dest)
  70 {
  71    int i,j;
  72
  73    while (i<N && (source[i])==0) i++;
  74    while (j<N && (dest[j])==0) j++;
  75
  76    dest[j-1] = source[i];
  77    source[i] = 0;
  78    PrintAll();       /* Print configuration after each move. */
  79    return dest[j-1];
  80 }
  81
  82
  83 /* Moves first n nonzero numbers from source to dest using the rules of Hanoi.
  84    Calls itself recursively.
  85    */
  86 void Hanoi(int n,int *source, int *dest, int *spare)
  87 {
  88    int i;
  89    if(n==1){
  90       Move(source,dest);
  91       return;
  92    }
  93
  94    Hanoi(n-1,source,spare,dest);
  95    Move(source,dest);
  96    Hanoi(n-1,spare,dest,source);
  97    return;
  98 }
  99
 100 int main()
 101 {
 102    int i;
 103
 104    /* initialize the towers */
 105    for(i=0;i<N;i++)A[i]=i+1;
 106    for(i=0;i<N;i++)B[i]=0;
 107    for(i=0;i<N;i++)C[i]=0;
 108
 109    printf("Solution of Tower of Hanoi Problem with %d Disks\n\n",N);
 110
 111    /* Print the starting state */
 112    printf("Starting state:\n");
 113    PrintAll();
 114    printf("\n\nSubsequent states:\n\n");
 115
 116    /* Do it! Use A = Source, B = Destination, C = Spare */
 117    Hanoi(N,A,B,C);
 118
 119    return 0;
 120 }
 121
 122 /* vim: set expandtab ts=4 sw=3 sts=3 tw=80 :*/