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 int *snew_dsf(int size)
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 */
75 /*print_dsf(ret, size); */
80 int dsf_canonify(int *dsf, int index)
82 return edsf_canonify(dsf, index, NULL);
85 void dsf_merge(int *dsf, int v1, int v2)
87 edsf_merge(dsf, v1, v2, FALSE);
90 int edsf_canonify(int *dsf, int index, int *inverse_return)
92 int start_index = index, canonical_index;
95 /* fprintf(stderr, "dsf = %p\n", dsf); */
96 /* fprintf(stderr, "Canonify %2d\n", index); */
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); */
109 canonical_index = index;
112 *inverse_return = inverse;
114 /* Update every member of this 'equivalence class' to point directly at the
115 * canonical member. */
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;
125 assert(inverse == 0);
127 /* fprintf(stderr, "Return %2d\n", index); */
132 void edsf_merge(int *dsf, int v1, int v2, int inverse)
136 /* fprintf(stderr, "dsf = %p\n", dsf); */
137 /* fprintf(stderr, "Merge [%2d,%2d], %d\n", v1, v2, inverse); */
139 v1 = edsf_canonify(dsf, v1, &i1);
141 v2 = edsf_canonify(dsf, v2, &i2);
144 /* fprintf(stderr, "Doing [%2d,%2d], %d\n", v1, v2, inverse); */
149 dsf[v2] = (v1 << 1) | !!inverse;
151 v2 = edsf_canonify(dsf, v2, &i2);
153 assert(i2 == inverse);
155 /* fprintf(stderr, "dsf[%2d] = %2d\n", v2, dsf[v2]); */