Commit | Line | Data |
---|---|---|
3b600ead TL |
1 | /* topological sort |
2 | * input is sequence of pairs of items (blank-free strings) | |
3 | * nonidentical pair is a directed edge in graph | |
4 | * identical pair merely indicates presence of node | |
5 | * output is ordered list of items consistent with | |
6 | * the partial ordering specified by the graph | |
7 | */ | |
8 | #include "stdio.h" | |
9 | ||
10 | /* the nodelist always has an empty element at the end to | |
11 | * make it easy to grow in natural order | |
12 | * states of the "live" field:*/ | |
13 | #define DEAD 0 /* already printed*/ | |
14 | #define LIVE 1 /* not yet printed*/ | |
15 | #define VISITED 2 /*used only in findloop()*/ | |
16 | ||
17 | struct nodelist { | |
18 | struct nodelist *nextnode; | |
19 | struct predlist *inedges; | |
20 | char *name; | |
21 | int live; | |
22 | } firstnode = {NULL, NULL, NULL, DEAD}; | |
23 | ||
24 | /* a predecessor list tells all the immediate | |
25 | * predecessors of a given node | |
26 | */ | |
27 | struct predlist { | |
28 | struct predlist *nextpred; | |
29 | struct nodelist *pred; | |
30 | }; | |
31 | ||
32 | struct nodelist *index(); | |
33 | struct nodelist *findloop(); | |
34 | struct nodelist *mark(); | |
35 | char *malloc(); | |
36 | char *empty = ""; | |
37 | ||
38 | /* the first for loop reads in the graph, | |
39 | * the second prints out the ordering | |
40 | */ | |
41 | main(argc,argv) | |
42 | char **argv; | |
43 | { | |
44 | register struct predlist *t; | |
45 | FILE *input = stdin; | |
46 | register struct nodelist *i, *j; | |
47 | int x; | |
48 | char precedes[50], follows[50]; | |
49 | if(argc>1) { | |
50 | input = fopen(argv[1],"r"); | |
51 | if(input==NULL) | |
52 | error("cannot open ", argv[1]); | |
53 | } | |
54 | for(;;) { | |
55 | x = fscanf(input,"%s%s",precedes, follows); | |
56 | if(x==EOF) | |
57 | break; | |
58 | if(x!=2) | |
59 | error("odd data",empty); | |
60 | i = index(precedes); | |
61 | j = index(follows); | |
62 | if(i==j||present(i,j)) | |
63 | continue; | |
64 | t = (struct predlist *)malloc(sizeof(struct predlist)); | |
65 | t->nextpred = j->inedges; | |
66 | t->pred = i; | |
67 | j->inedges = t; | |
68 | } | |
69 | for(;;) { | |
70 | x = 0; /*anything LIVE on this sweep?*/ | |
71 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) { | |
72 | if(i->live==LIVE) { | |
73 | x = 1; | |
74 | if(!anypred(i)) | |
75 | break; | |
76 | } | |
77 | } | |
78 | if(x==0) | |
79 | break; | |
80 | if(i->nextnode==NULL) | |
81 | i = findloop(); | |
82 | printf("%s\n",i->name); | |
83 | i->live = DEAD; | |
84 | } | |
85 | } | |
86 | ||
87 | /* is i present on j's predecessor list? | |
88 | */ | |
89 | present(i,j) | |
90 | struct nodelist *i, *j; | |
91 | { | |
92 | register struct predlist *t; | |
93 | for(t=j->inedges; t!=NULL; t=t->nextpred) | |
94 | if(t->pred==i) | |
95 | return(1); | |
96 | return(0); | |
97 | } | |
98 | ||
99 | /* is there any live predecessor for i? | |
100 | */ | |
101 | anypred(i) | |
102 | struct nodelist *i; | |
103 | { | |
104 | register struct predlist *t; | |
105 | for(t=i->inedges; t!=NULL; t=t->nextpred) | |
106 | if(t->pred->live==LIVE) | |
107 | return(1); | |
108 | return(0); | |
109 | } | |
110 | ||
111 | /* turn a string into a node pointer | |
112 | */ | |
113 | struct nodelist * | |
114 | index(s) | |
115 | register char *s; | |
116 | { | |
117 | register struct nodelist *i; | |
118 | register char *t; | |
119 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) | |
120 | if(cmp(s,i->name)) | |
121 | return(i); | |
122 | for(t=s; *t; t++) ; | |
123 | t = malloc((unsigned)(t+1-s)); | |
124 | i->nextnode = (struct nodelist *)malloc(sizeof(struct nodelist)); | |
125 | if(i->nextnode==NULL||t==NULL) | |
126 | error("too many items",empty); | |
127 | i->name = t; | |
128 | i->live = LIVE; | |
129 | i->nextnode->nextnode = NULL; | |
130 | i->nextnode->inedges = NULL; | |
131 | i->nextnode->live = DEAD; | |
132 | while(*t++ = *s++); | |
133 | return(i); | |
134 | } | |
135 | ||
136 | cmp(s,t) | |
137 | register char *s, *t; | |
138 | { | |
139 | while(*s==*t) { | |
140 | if(*s==0) | |
141 | return(1); | |
142 | s++; | |
143 | t++; | |
144 | } | |
145 | return(0); | |
146 | } | |
147 | ||
148 | error(s,t) | |
149 | char *s, *t; | |
150 | { | |
151 | note(s,t); | |
152 | exit(1); | |
153 | } | |
154 | ||
155 | note(s,t) | |
156 | char *s,*t; | |
157 | { | |
158 | fprintf(stderr,"tsort: %s%s\n",s,t); | |
159 | } | |
160 | ||
161 | /* given that there is a cycle, find some | |
162 | * node in it | |
163 | */ | |
164 | struct nodelist * | |
165 | findloop() | |
166 | { | |
167 | register struct nodelist *i, *j; | |
168 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) | |
169 | if(i->live==LIVE) | |
170 | break; | |
171 | note("cycle in data",empty); | |
172 | i = mark(i); | |
173 | if(i==NULL) | |
174 | error("program error",empty); | |
175 | for(j= &firstnode; j->nextnode!=NULL; j=j->nextnode) | |
176 | if(j->live==VISITED) | |
177 | j->live = LIVE; | |
178 | return(i); | |
179 | } | |
180 | ||
181 | /* depth-first search of LIVE predecessors | |
182 | * to find some element of a cycle; | |
183 | * VISITED is a temporary state recording the | |
184 | * visits of the search | |
185 | */ | |
186 | struct nodelist * | |
187 | mark(i) | |
188 | register struct nodelist *i; | |
189 | { | |
190 | register struct nodelist *j; | |
191 | register struct predlist *t; | |
192 | if(i->live==DEAD) | |
193 | return(NULL); | |
194 | if(i->live==VISITED) | |
195 | return(i); | |
196 | i->live = VISITED; | |
197 | for(t=i->inedges; t!=NULL; t=t->nextpred) { | |
198 | j = mark(t->pred); | |
199 | if(j!=NULL) { | |
200 | note(i->name,empty); | |
201 | return(j); | |
202 | } | |
203 | } | |
204 | return(NULL); | |
205 | } |