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1 | /* |
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2 | * dsf.c: some functions to handle a disjoint set forest, |
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3 | * which is a data structure useful in any solver which has to |
4 | * worry about avoiding closed loops. |
5 | */ |
6 | |
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7 | #include <assert.h> |
8 | #include <string.h> |
9 | |
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10 | #include "puzzles.h" |
11 | |
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12 | /*void print_dsf(int *dsf, int size) |
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13 | { |
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14 | int *printed_elements = snewn(size, int); |
15 | int *equal_elements = snewn(size, int); |
16 | int *inverse_elements = snewn(size, int); |
17 | int printed_count = 0, equal_count, inverse_count; |
18 | int i, n, inverse; |
19 | |
20 | memset(printed_elements, -1, sizeof(int) * size); |
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21 | |
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22 | while (1) { |
23 | equal_count = 0; |
24 | inverse_count = 0; |
25 | for (i = 0; i < size; ++i) { |
26 | if (!memchr(printed_elements, i, sizeof(int) * size)) |
27 | break; |
28 | } |
29 | if (i == size) |
30 | goto done; |
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31 | |
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32 | i = dsf_canonify(dsf, i); |
33 | |
34 | for (n = 0; n < size; ++n) { |
35 | if (edsf_canonify(dsf, n, &inverse) == i) { |
36 | if (inverse) |
37 | inverse_elements[inverse_count++] = n; |
38 | else |
39 | equal_elements[equal_count++] = n; |
40 | } |
41 | } |
42 | |
43 | for (n = 0; n < equal_count; ++n) { |
44 | fprintf(stderr, "%d ", equal_elements[n]); |
45 | printed_elements[printed_count++] = equal_elements[n]; |
46 | } |
47 | if (inverse_count) { |
48 | fprintf(stderr, "!= "); |
49 | for (n = 0; n < inverse_count; ++n) { |
50 | fprintf(stderr, "%d ", inverse_elements[n]); |
51 | printed_elements[printed_count++] = inverse_elements[n]; |
52 | } |
53 | } |
54 | fprintf(stderr, "\n"); |
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55 | } |
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56 | done: |
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57 | |
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58 | sfree(printed_elements); |
59 | sfree(equal_elements); |
60 | sfree(inverse_elements); |
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61 | }*/ |
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62 | |
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63 | void dsf_init(int *dsf, int size) |
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64 | { |
65 | int i; |
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66 | |
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67 | for (i = 0; i < size; i++) { |
68 | /* Bottom bit of each element of this array stores whether that element |
69 | * is opposite to its parent, which starts off as false */ |
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70 | dsf[i] = i << 1; |
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71 | } |
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72 | } |
73 | |
74 | int *snew_dsf(int size) |
75 | { |
76 | int *ret; |
77 | |
78 | ret = snewn(size, int); |
79 | dsf_init(ret, size); |
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80 | |
81 | /*print_dsf(ret, size); */ |
82 | |
83 | return ret; |
84 | } |
85 | |
86 | int dsf_canonify(int *dsf, int index) |
87 | { |
88 | return edsf_canonify(dsf, index, NULL); |
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89 | } |
90 | |
91 | void dsf_merge(int *dsf, int v1, int v2) |
92 | { |
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93 | edsf_merge(dsf, v1, v2, FALSE); |
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94 | } |
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95 | |
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96 | int edsf_canonify(int *dsf, int index, int *inverse_return) |
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97 | { |
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98 | int start_index = index, canonical_index; |
99 | int inverse = 0; |
100 | |
101 | /* fprintf(stderr, "dsf = %p\n", dsf); */ |
102 | /* fprintf(stderr, "Canonify %2d\n", index); */ |
103 | |
104 | assert(index >= 0); |
105 | |
106 | /* Find the index of the canonical element of the 'equivalence class' of |
107 | * which start_index is a member, and figure out whether start_index is the |
108 | * same as or inverse to that. */ |
109 | while ((dsf[index] >> 1) != index) { |
110 | inverse ^= (dsf[index] & 1); |
111 | index = dsf[index] >> 1; |
112 | /* fprintf(stderr, "index = %2d, ", index); */ |
113 | /* fprintf(stderr, "inverse = %d\n", inverse); */ |
114 | } |
115 | canonical_index = index; |
116 | |
117 | if (inverse_return) |
118 | *inverse_return = inverse; |
119 | |
120 | /* Update every member of this 'equivalence class' to point directly at the |
121 | * canonical member. */ |
122 | index = start_index; |
123 | while (index != canonical_index) { |
124 | int nextindex = dsf[index] >> 1; |
125 | int nextinverse = inverse ^ (dsf[index] & 1); |
126 | dsf[index] = (canonical_index << 1) | inverse; |
127 | inverse = nextinverse; |
128 | index = nextindex; |
129 | } |
130 | |
131 | assert(inverse == 0); |
132 | |
133 | /* fprintf(stderr, "Return %2d\n", index); */ |
134 | |
135 | return index; |
136 | } |
137 | |
138 | void edsf_merge(int *dsf, int v1, int v2, int inverse) |
139 | { |
140 | int i1, i2; |
141 | |
142 | /* fprintf(stderr, "dsf = %p\n", dsf); */ |
143 | /* fprintf(stderr, "Merge [%2d,%2d], %d\n", v1, v2, inverse); */ |
144 | |
145 | v1 = edsf_canonify(dsf, v1, &i1); |
146 | inverse ^= i1; |
147 | v2 = edsf_canonify(dsf, v2, &i2); |
148 | inverse ^= i2; |
149 | |
150 | /* fprintf(stderr, "Doing [%2d,%2d], %d\n", v1, v2, inverse); */ |
151 | |
152 | if (v1 == v2) |
153 | assert(!inverse); |
154 | else |
155 | dsf[v2] = (v1 << 1) | !!inverse; |
156 | |
157 | v2 = edsf_canonify(dsf, v2, &i2); |
158 | assert(v2 == v1); |
159 | assert(i2 == inverse); |
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160 | |
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161 | /* fprintf(stderr, "dsf[%2d] = %2d\n", v2, dsf[v2]); */ |
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162 | } |