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