summaryrefslogtreecommitdiffstats
path: root/tsort.scm
diff options
context:
space:
mode:
Diffstat (limited to 'tsort.scm')
-rw-r--r--tsort.scm58
1 files changed, 53 insertions, 5 deletions
diff --git a/tsort.scm b/tsort.scm
index 9371f3c..9db98f2 100644
--- a/tsort.scm
+++ b/tsort.scm
@@ -1,7 +1,6 @@
;;; "tsort.scm" Topological sort
;;; Copyright (C) 1995 Mikael Djurfeldt
-;
-; This code is in the public domain.
+;;; This code is in the public domain.
;;; The algorithm is inspired by Cormen, Leiserson and Rivest (1990)
;;; "Introduction to Algorithms", chapter 23
@@ -9,7 +8,57 @@
(require 'hash-table)
(require 'primes)
-(define (topological-sort dag pred)
+;;@code{(require 'topological-sort)} or @code{(require 'tsort)}
+;;@ftindex topological-sort
+;;@ftindex tsort
+
+;;@noindent
+;;The algorithm is inspired by Cormen, Leiserson and Rivest (1990)
+;;@cite{Introduction to Algorithms}, chapter 23.
+
+;;@body
+;;@defunx topological-sort dag pred
+;;where
+;;@table @var
+;;@item dag
+;;is a list of sublists. The car of each sublist is a vertex. The cdr is
+;;the adjacency list of that vertex, i.e. a list of all vertices to which
+;;there exists an edge from the car vertex.
+;;@item pred
+;;is one of @code{eq?}, @code{eqv?}, @code{equal?}, @code{=},
+;;@code{char=?}, @code{char-ci=?}, @code{string=?}, or @code{string-ci=?}.
+;;@end table
+;;
+;;Sort the directed acyclic graph @1 so that for every edge from
+;;vertex @var{u} to @var{v}, @var{u} will come before @var{v} in the
+;;resulting list of vertices.
+;;
+;;Time complexity: O (|V| + |E|)
+;;
+;;Example (from Cormen):
+;;@quotation
+;;Prof. Bumstead topologically sorts his clothing when getting
+;;dressed. The first argument to @0 describes which
+;;garments he needs to put on before others. (For example,
+;;Prof Bumstead needs to put on his shirt before he puts on his
+;;tie or his belt.) @0 gives the correct order of dressing:
+;;@end quotation
+;;
+;;@example
+;;(require 'tsort)
+;;@ftindex tsort
+;;(tsort '((shirt tie belt)
+;; (tie jacket)
+;; (belt jacket)
+;; (watch)
+;; (pants shoes belt)
+;; (undershorts pants shoes)
+;; (socks shoes))
+;; eq?)
+;;@result{}
+;;(socks undershorts pants shoes watch shirt belt tie jacket)
+;;@end example
+(define (tsort dag pred)
(if (null? dag)
'()
(let* ((adj-table (make-hash-table
@@ -42,5 +91,4 @@
(visit (car def) (cdr def)))))
(cdr dag)))
sorted)))
-
-(define tsort topological-sort)
+(define topological-sort tsort)