Commit | Line | Data |
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dc5d5eb8 BJ |
1 | static char *sccsid = "@(#)tsort.c 4.1 (Berkeley) %G%"; |
2 | /* topological sort | |
3 | * input is sequence of pairs of items (blank-free strings) | |
4 | * nonidentical pair is a directed edge in graph | |
5 | * identical pair merely indicates presence of node | |
6 | * output is ordered list of items consistent with | |
7 | * the partial ordering specified by the graph | |
8 | */ | |
9 | #include "stdio.h" | |
10 | ||
11 | /* the nodelist always has an empty element at the end to | |
12 | * make it easy to grow in natural order | |
13 | * states of the "live" field:*/ | |
14 | #define DEAD 0 /* already printed*/ | |
15 | #define LIVE 1 /* not yet printed*/ | |
16 | #define VISITED 2 /*used only in findloop()*/ | |
17 | ||
18 | struct nodelist { | |
19 | struct nodelist *nextnode; | |
20 | struct predlist *inedges; | |
21 | char *name; | |
22 | int live; | |
23 | } firstnode = {NULL, NULL, NULL, DEAD}; | |
24 | ||
25 | /* a predecessor list tells all the immediate | |
26 | * predecessors of a given node | |
27 | */ | |
28 | struct predlist { | |
29 | struct predlist *nextpred; | |
30 | struct nodelist *pred; | |
31 | }; | |
32 | ||
33 | struct nodelist *index(); | |
34 | struct nodelist *findloop(); | |
35 | struct nodelist *mark(); | |
36 | char *malloc(); | |
37 | char *empty = ""; | |
38 | ||
39 | /* the first for loop reads in the graph, | |
40 | * the second prints out the ordering | |
41 | */ | |
42 | main(argc,argv) | |
43 | char **argv; | |
44 | { | |
45 | register struct predlist *t; | |
46 | FILE *input = stdin; | |
47 | register struct nodelist *i, *j; | |
48 | int x; | |
49 | char precedes[50], follows[50]; | |
50 | if(argc>1) { | |
51 | input = fopen(argv[1],"r"); | |
52 | if(input==NULL) | |
53 | error("cannot open ", argv[1]); | |
54 | } | |
55 | for(;;) { | |
56 | x = fscanf(input,"%s%s",precedes, follows); | |
57 | if(x==EOF) | |
58 | break; | |
59 | if(x!=2) | |
60 | error("odd data",empty); | |
61 | i = index(precedes); | |
62 | j = index(follows); | |
63 | if(i==j||present(i,j)) | |
64 | continue; | |
65 | t = (struct predlist *)malloc(sizeof(struct predlist)); | |
66 | t->nextpred = j->inedges; | |
67 | t->pred = i; | |
68 | j->inedges = t; | |
69 | } | |
70 | for(;;) { | |
71 | x = 0; /*anything LIVE on this sweep?*/ | |
72 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) { | |
73 | if(i->live==LIVE) { | |
74 | x = 1; | |
75 | if(!anypred(i)) | |
76 | break; | |
77 | } | |
78 | } | |
79 | if(x==0) | |
80 | break; | |
81 | if(i->nextnode==NULL) | |
82 | i = findloop(); | |
83 | printf("%s\n",i->name); | |
84 | i->live = DEAD; | |
85 | } | |
86 | } | |
87 | ||
88 | /* is i present on j's predecessor list? | |
89 | */ | |
90 | present(i,j) | |
91 | struct nodelist *i, *j; | |
92 | { | |
93 | register struct predlist *t; | |
94 | for(t=j->inedges; t!=NULL; t=t->nextpred) | |
95 | if(t->pred==i) | |
96 | return(1); | |
97 | return(0); | |
98 | } | |
99 | ||
100 | /* is there any live predecessor for i? | |
101 | */ | |
102 | anypred(i) | |
103 | struct nodelist *i; | |
104 | { | |
105 | register struct predlist *t; | |
106 | for(t=i->inedges; t!=NULL; t=t->nextpred) | |
107 | if(t->pred->live==LIVE) | |
108 | return(1); | |
109 | return(0); | |
110 | } | |
111 | ||
112 | /* turn a string into a node pointer | |
113 | */ | |
114 | struct nodelist * | |
115 | index(s) | |
116 | register char *s; | |
117 | { | |
118 | register struct nodelist *i; | |
119 | register char *t; | |
120 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) | |
121 | if(cmp(s,i->name)) | |
122 | return(i); | |
123 | for(t=s; *t; t++) ; | |
124 | t = malloc((unsigned)(t+1-s)); | |
125 | i->nextnode = (struct nodelist *)malloc(sizeof(struct nodelist)); | |
126 | if(i->nextnode==NULL||t==NULL) | |
127 | error("too many items",empty); | |
128 | i->name = t; | |
129 | i->live = LIVE; | |
130 | i->nextnode->nextnode = NULL; | |
131 | i->nextnode->inedges = NULL; | |
132 | i->nextnode->live = DEAD; | |
133 | while(*t++ = *s++); | |
134 | return(i); | |
135 | } | |
136 | ||
137 | cmp(s,t) | |
138 | register char *s, *t; | |
139 | { | |
140 | while(*s==*t) { | |
141 | if(*s==0) | |
142 | return(1); | |
143 | s++; | |
144 | t++; | |
145 | } | |
146 | return(0); | |
147 | } | |
148 | ||
149 | error(s,t) | |
150 | char *s, *t; | |
151 | { | |
152 | note(s,t); | |
153 | exit(1); | |
154 | } | |
155 | ||
156 | note(s,t) | |
157 | char *s,*t; | |
158 | { | |
159 | fprintf(stderr,"tsort: %s%s\n",s,t); | |
160 | } | |
161 | ||
162 | /* given that there is a cycle, find some | |
163 | * node in it | |
164 | */ | |
165 | struct nodelist * | |
166 | findloop() | |
167 | { | |
168 | register struct nodelist *i, *j; | |
169 | for(i= &firstnode; i->nextnode!=NULL; i=i->nextnode) | |
170 | if(i->live==LIVE) | |
171 | break; | |
172 | note("cycle in data",empty); | |
173 | i = mark(i); | |
174 | if(i==NULL) | |
175 | error("program error",empty); | |
176 | for(j= &firstnode; j->nextnode!=NULL; j=j->nextnode) | |
177 | if(j->live==VISITED) | |
178 | j->live = LIVE; | |
179 | return(i); | |
180 | } | |
181 | ||
182 | /* depth-first search of LIVE predecessors | |
183 | * to find some element of a cycle; | |
184 | * VISITED is a temporary state recording the | |
185 | * visits of the search | |
186 | */ | |
187 | struct nodelist * | |
188 | mark(i) | |
189 | register struct nodelist *i; | |
190 | { | |
191 | register struct nodelist *j; | |
192 | register struct predlist *t; | |
193 | if(i->live==DEAD) | |
194 | return(NULL); | |
195 | if(i->live==VISITED) | |
196 | return(i); | |
197 | i->live = VISITED; | |
198 | for(t=i->inedges; t!=NULL; t=t->nextpred) { | |
199 | j = mark(t->pred); | |
200 | if(j!=NULL) { | |
201 | note(i->name,empty); | |
202 | return(j); | |
203 | } | |
204 | } | |
205 | return(NULL); | |
206 | } |