Commit | Line | Data |
---|---|---|
18d73507 KT |
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 | */ | |
13 | ||
14 | struct nodelist { | |
15 | struct nodelist *nextnode; | |
16 | struct predlist *inedges; | |
17 | char *name; | |
18 | enum {DEAD, LIVE, ONCE, TWICE} live; | |
19 | } firstnode = {NULL, NULL, NULL, DEAD}; | |
20 | ||
21 | /* a predecessor list tells all the immediate | |
22 | * predecessors of a given node | |
23 | */ | |
24 | struct predlist { | |
25 | struct predlist *nextpred; | |
26 | struct nodelist *pred; | |
27 | }; | |
28 | ||
29 | struct nodelist *index(); | |
30 | struct nodelist *findloop(); | |
31 | struct nodelist *mark(); | |
32 | char *malloc(); | |
33 | char *empty = ""; | |
34 | ||
35 | /* the first for loop reads in the graph, | |
36 | * the second prints out the ordering | |
37 | */ | |
38 | main(argc,argv) | |
39 | char **argv; | |
40 | { | |
41 | register struct predlist *t; | |
42 | FILE *input = stdin; | |
43 | register struct nodelist *i, *j; | |
44 | int x; | |
45 | char precedes[50], follows[50]; | |
46 | if(argc>1) { | |
47 | input = fopen(argv[1],"r"); | |
48 | if(input==NULL) | |
49 | error("cannot open ", argv[1]); | |
50 | } | |
51 | for(;;) { | |
52 | x = fscanf(input,"%s%s",precedes, follows); | |
53 | if(x==EOF) | |
54 | break; | |
55 | if(x!=2) | |
56 | error("odd data",empty); | |
57 | i = index(precedes); | |
58 | j = index(follows); | |
59 | if(i==j||present(i,j)) | |
60 | continue; | |
61 | t = (struct predlist *)malloc(sizeof(struct predlist)); | |
62 | t->nextpred = j->inedges; | |
63 | t->pred = i; | |
64 | j->inedges = t; | |
65 | } | |
66 | for(;;) { | |
67 | x = 0; /*anything LIVE on this sweep?*/ | |
68 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) { | |
69 | if(i->live==LIVE) { | |
70 | x = 1; | |
71 | if(!anypred(i)) | |
72 | break; | |
73 | } | |
74 | } | |
75 | if(x==0) | |
76 | break; | |
77 | if(i->nextnode==NULL) | |
78 | i = findloop(); | |
79 | printf("%s\n",i->name); | |
80 | i->live = DEAD; | |
81 | } | |
82 | } | |
83 | ||
84 | /* is i present on j's predecessor list? | |
85 | */ | |
86 | present(i,j) | |
87 | struct nodelist *i, *j; | |
88 | { | |
89 | register struct predlist *t; | |
90 | for(t=j->inedges; t!=NULL; t=t->nextpred) | |
91 | if(t->pred==i) | |
92 | return(1); | |
93 | return(0); | |
94 | } | |
95 | ||
96 | /* is there any live predecessor for i? | |
97 | */ | |
98 | anypred(i) | |
99 | struct nodelist *i; | |
100 | { | |
101 | register struct predlist *t; | |
102 | for(t=i->inedges; t!=NULL; t=t->nextpred) | |
103 | if(t->pred->live==LIVE) | |
104 | return(1); | |
105 | return(0); | |
106 | } | |
107 | ||
108 | /* turn a string into a node pointer | |
109 | */ | |
110 | struct nodelist * | |
111 | index(s) | |
112 | register char *s; | |
113 | { | |
114 | register struct nodelist *i; | |
115 | register char *t; | |
116 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) | |
117 | if(cmp(s,i->name)) | |
118 | return(i); | |
119 | for(t=s; *t; t++) ; | |
120 | t = malloc((unsigned)(t+1-s)); | |
121 | i->nextnode = (struct nodelist *)malloc(sizeof(struct nodelist)); | |
122 | if(i->nextnode==NULL||t==NULL) | |
123 | error("too many items",empty); | |
124 | i->name = t; | |
125 | i->live = LIVE; | |
126 | i->nextnode->nextnode = NULL; | |
127 | i->nextnode->inedges = NULL; | |
128 | i->nextnode->live = DEAD; | |
129 | while(*t++ = *s++); | |
130 | return(i); | |
131 | } | |
132 | ||
133 | cmp(s,t) | |
134 | register char *s, *t; | |
135 | { | |
136 | while(*s==*t) { | |
137 | if(*s==0) | |
138 | return(1); | |
139 | s++; | |
140 | t++; | |
141 | } | |
142 | return(0); | |
143 | } | |
144 | ||
145 | error(s,t) | |
146 | char *s, *t; | |
147 | { | |
148 | note(s,t); | |
149 | exit(1); | |
150 | } | |
151 | ||
152 | note(s,t) | |
153 | char *s,*t; | |
154 | { | |
155 | fprintf(stderr,"tsort: %s%s\n",s,t); | |
156 | } | |
157 | ||
158 | /* given that there is a cycle, find some | |
159 | * node in it | |
160 | */ | |
161 | struct nodelist * | |
162 | findloop() | |
163 | { | |
164 | register struct nodelist *i, *j; | |
165 | register struct predlist *p; | |
166 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) | |
167 | if(i->live==LIVE) | |
168 | break; | |
169 | note("cycle in reverse order",empty); | |
170 | while(i->live==LIVE) { | |
171 | i->live = ONCE; | |
172 | for(p=i->inedges; ; p=p->nextpred) { | |
173 | if(p==NULL) | |
174 | error("error 1"); | |
175 | i = p->pred; | |
176 | if(i->live!=DEAD) | |
177 | break; | |
178 | } | |
179 | } | |
180 | while(i->live==ONCE) { | |
181 | i->live = TWICE; | |
182 | note(i->name,empty); | |
183 | for(p=i->inedges; ; p=p->nextpred) { | |
184 | if(p==NULL) | |
185 | error("error 2"); | |
186 | i = p->pred; | |
187 | if(i->live!=DEAD) | |
188 | break; | |
189 | } | |
190 | } | |
191 | for(j= &firstnode; j->nextnode!=NULL; j=j->nextnode) | |
192 | if(j->live!=DEAD) | |
193 | j->live = LIVE; | |
194 | return(i); | |
195 | } | |
196 |