Dijkstra's algorithm: Difference between revisions
no edit summary
(→{{header|Tailspin}}: Update to stricter typing) |
No edit summary |
||
Line 2,041:
5: distance = 11, 0 --> 2 --> 5
</pre>
=={{header|Emacs Lisp}}==
<lang lisp>
(setq path-list `(
(a b ,nil 7)
(a c ,nil 9)
(a f ,nil 14)
(b c ,nil 10)
(b d ,nil 15)
(c d ,nil 11)
(c f ,nil 2)
(d e ,nil 6)
(e f ,nil 9)
))
(defun calculate-shortest-path ()
(let ((shortest-path '())
(head-point (nth 0 (nth 0 path-list))))
(defun combine-new-path (path1 path2)
(list (nth 0 path1) (nth 1 path2) (nth 0 path2)
(+ (nth 3 path1) (nth 3 path2))) )
(defun find-shortest-path (start end)
(catch 'result-found
(mapcar (lambda (item)
(when (and (eq (nth 0 item) start) (eq (nth 1 item) end))
(throw 'result-found item))
) shortest-path)
nil
)
)
(defun find-shortest-route (start end)
(let ((point-list '())
(end-point end)
path-found)
(add-to-list 'point-list end)
(catch 'no-more-path
(while 't
(setq path-found (find-shortest-path start end-point))
(if (or (not path-found) (not (nth 2 path-found)))
(throw 'no-more-path nil)
(progn
(add-to-list 'point-list (nth 2 path-found))
(setq end-point (nth 2 path-found)) )
)
)
)
(add-to-list 'point-list start)
)
)
(defun add-shortest-path (item)
(add-to-list 'shortest-path item) )
(defun process-path (path)
(if (eq head-point (nth 0 path))
(add-to-list 'shortest-path path)
(progn
(dolist (spath shortest-path)
(when (eq (nth 1 spath) (nth 0 path))
(let* ((new-path (combine-new-path spath path))
(spath-found (find-shortest-path (nth 0 new-path)
(nth 1 new-path))))
(if spath-found
(when (< (nth 3 new-path) (nth 3 spath-found))
(setcdr (nthcdr 1 spath-found) (list (nth 2 new-path) (nth 3 new-path)))
)
(add-shortest-path new-path)) ) ) ) ) ) )
(defun show-shortest-path (start end)
(let ((path-found (find-shortest-path start end))
(route-found (find-shortest-route start end)))
(if path-found
(progn
(message "shortest distance: %s" (nth 3 path-found))
(message "shortest route: %s" route-found) )
(message "shortest path not found") )
)
(message "--") )
(dolist (path path-list)
(process-path path) )
(message "from %s to %s:" 'a 'e)
(show-shortest-path 'a 'e)
(message "from %s to %s:" 'a 'f)
(show-shortest-path 'a 'f)
)
)
(calculate-shortest-path)
</lisp>
outputs:
<pre>from a to e:
shortest distance: 26
shortest route: (a c d e)
--
from a to f:
shortest distance: 11
shortest route: (a c f)
--</pre>
=={{header|Erlang}}==
| |||