2 * dsf.c: some functions to handle a disjoint set forest,
3 * which is a data structure useful in any solver which has to
4 * worry about avoiding closed loops.
12 void print_dsf(int *dsf, int size)
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;
20 memset(printed_elements, -1, sizeof(int) * size);
25 for (i = 0; i < size; ++i) {
26 if (!memchr(printed_elements, i, sizeof(int) * size))
32 i = dsf_canonify(dsf, i);
34 for (n = 0; n < size; ++n) {
35 if (edsf_canonify(dsf, n, &inverse) == i) {
37 inverse_elements[inverse_count++] = n;
39 equal_elements[equal_count++] = n;
43 for (n = 0; n < equal_count; ++n) {
44 fprintf(stderr, "%d ", equal_elements[n]);
45 printed_elements[printed_count++] = equal_elements[n];
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];
54 fprintf(stderr, "\n");
58 sfree(printed_elements);
59 sfree(equal_elements);
60 sfree(inverse_elements);
63 void dsf_init(int *dsf, int size)
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 */
74 int *snew_dsf(int size)
78 ret = snewn(size, int);
81 /*print_dsf(ret, size); */
86 int dsf_canonify(int *dsf, int index)
88 return edsf_canonify(dsf, index, NULL);
91 void dsf_merge(int *dsf, int v1, int v2)
93 edsf_merge(dsf, v1, v2, FALSE);
96 int edsf_canonify(int *dsf, int index, int *inverse_return)
98 int start_index = index, canonical_index;
101 /* fprintf(stderr, "dsf = %p\n", dsf); */
102 /* fprintf(stderr, "Canonify %2d\n", index); */
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); */
115 canonical_index = index;
118 *inverse_return = inverse;
120 /* Update every member of this 'equivalence class' to point directly at the
121 * canonical member. */
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;
131 assert(inverse == 0);
133 /* fprintf(stderr, "Return %2d\n", index); */
138 void edsf_merge(int *dsf, int v1, int v2, int inverse)
142 /* fprintf(stderr, "dsf = %p\n", dsf); */
143 /* fprintf(stderr, "Merge [%2d,%2d], %d\n", v1, v2, inverse); */
145 v1 = edsf_canonify(dsf, v1, &i1);
147 v2 = edsf_canonify(dsf, v2, &i2);
150 /* fprintf(stderr, "Doing [%2d,%2d], %d\n", v1, v2, inverse); */
155 dsf[v2] = (v1 << 1) | !!inverse;
157 v2 = edsf_canonify(dsf, v2, &i2);
159 assert(i2 == inverse);
161 /* fprintf(stderr, "dsf[%2d] = %2d\n", v2, dsf[v2]); */