f1010613 |
1 | /* |
121aae4b |
2 | * dsf.c: some functions to handle a disjoint set forest, |
f1010613 |
3 | * which is a data structure useful in any solver which has to |
4 | * worry about avoiding closed loops. |
5 | */ |
6 | |
121aae4b |
7 | #include <assert.h> |
8 | #include <string.h> |
9 | |
986cc2de |
10 | #include "puzzles.h" |
11 | |
121aae4b |
12 | void print_dsf(int *dsf, int size) |
f1010613 |
13 | { |
121aae4b |
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); |
f1010613 |
21 | |
121aae4b |
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; |
f1010613 |
31 | |
121aae4b |
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"); |
f1010613 |
55 | } |
121aae4b |
56 | done: |
f1010613 |
57 | |
121aae4b |
58 | sfree(printed_elements); |
59 | sfree(equal_elements); |
60 | sfree(inverse_elements); |
61 | } |
62 | |
63 | int *snew_dsf(int size) |
64 | { |
65 | int i; |
66 | int *ret; |
67 | |
68 | ret = snewn(size, int); |
69 | for (i = 0; i < size; i++) { |
70 | /* Bottom bit of each element of this array stores whether that element |
71 | * is opposite to its parent, which starts off as false */ |
72 | ret[i] = i << 1; |
73 | } |
74 | |
75 | /*print_dsf(ret, size); */ |
76 | |
77 | return ret; |
78 | } |
79 | |
80 | int dsf_canonify(int *dsf, int index) |
81 | { |
82 | return edsf_canonify(dsf, index, NULL); |
f1010613 |
83 | } |
84 | |
85 | void dsf_merge(int *dsf, int v1, int v2) |
86 | { |
121aae4b |
87 | edsf_merge(dsf, v1, v2, FALSE); |
f1010613 |
88 | } |
66a74a18 |
89 | |
121aae4b |
90 | int edsf_canonify(int *dsf, int index, int *inverse_return) |
66a74a18 |
91 | { |
121aae4b |
92 | int start_index = index, canonical_index; |
93 | int inverse = 0; |
94 | |
95 | /* fprintf(stderr, "dsf = %p\n", dsf); */ |
96 | /* fprintf(stderr, "Canonify %2d\n", index); */ |
97 | |
98 | assert(index >= 0); |
99 | |
100 | /* Find the index of the canonical element of the 'equivalence class' of |
101 | * which start_index is a member, and figure out whether start_index is the |
102 | * same as or inverse to that. */ |
103 | while ((dsf[index] >> 1) != index) { |
104 | inverse ^= (dsf[index] & 1); |
105 | index = dsf[index] >> 1; |
106 | /* fprintf(stderr, "index = %2d, ", index); */ |
107 | /* fprintf(stderr, "inverse = %d\n", inverse); */ |
108 | } |
109 | canonical_index = index; |
110 | |
111 | if (inverse_return) |
112 | *inverse_return = inverse; |
113 | |
114 | /* Update every member of this 'equivalence class' to point directly at the |
115 | * canonical member. */ |
116 | index = start_index; |
117 | while (index != canonical_index) { |
118 | int nextindex = dsf[index] >> 1; |
119 | int nextinverse = inverse ^ (dsf[index] & 1); |
120 | dsf[index] = (canonical_index << 1) | inverse; |
121 | inverse = nextinverse; |
122 | index = nextindex; |
123 | } |
124 | |
125 | assert(inverse == 0); |
126 | |
127 | /* fprintf(stderr, "Return %2d\n", index); */ |
128 | |
129 | return index; |
130 | } |
131 | |
132 | void edsf_merge(int *dsf, int v1, int v2, int inverse) |
133 | { |
134 | int i1, i2; |
135 | |
136 | /* fprintf(stderr, "dsf = %p\n", dsf); */ |
137 | /* fprintf(stderr, "Merge [%2d,%2d], %d\n", v1, v2, inverse); */ |
138 | |
139 | v1 = edsf_canonify(dsf, v1, &i1); |
140 | inverse ^= i1; |
141 | v2 = edsf_canonify(dsf, v2, &i2); |
142 | inverse ^= i2; |
143 | |
144 | /* fprintf(stderr, "Doing [%2d,%2d], %d\n", v1, v2, inverse); */ |
145 | |
146 | if (v1 == v2) |
147 | assert(!inverse); |
148 | else |
149 | dsf[v2] = (v1 << 1) | !!inverse; |
150 | |
151 | v2 = edsf_canonify(dsf, v2, &i2); |
152 | assert(v2 == v1); |
153 | assert(i2 == inverse); |
66a74a18 |
154 | |
121aae4b |
155 | /* fprintf(stderr, "dsf[%2d] = %2d\n", v2, dsf[v2]); */ |
66a74a18 |
156 | } |