Maze solving
Maze solving is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.
For a maze generated by this task, write a function that finds (and displays) for a given cell the shortest path to the next exit. Note that because these mazes are generated by the Depth-first search algorithm, they contain no circular paths, and a simple depth-first tree search can be used.
PicoLisp
<lang PicoLisp>(de shortestExit (This Maze)
(let (Path NIL Best NIL)
(recur (This Path)
(when (and This (not (: mark)))
(push 'Path This)
(let Cell (val This)
(if (fish =T Cell)
(unless (and Best (>= (length Path) (length Best)))
(setq Best Path) )
(=: mark T)
(recurse (caar Cell) Path)
(recurse (cdar Cell) Path)
(recurse (cadr Cell) Path)
(recurse (cddr Cell) Path)
(=: mark NIL) ) ) ) )
(disp Maze 0
'((This) (if (memq This Best) " # " " ")) ) ) )</lang>
Output, using the maze produced in Maze generation#PicoLisp:
: (shortestExit 'a1 Maze)
+ +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
12 | # | # # | | | |
+ + + + + +---+ + +---+---+ + +---+ +---+ +
11 | # # | # | | | | | | | | |
+ +---+ +---+---+ +---+---+ + +---+---+ +---+ +---+
10 | | | # | | | | | | |
+ + + +---+ + + + + +---+---+ +---+ +---+ +
9 | | # # | | | | | | | | |
+ +---+---+ + +---+ +---+---+ + + + +---+ + +
8 | | # # | # | | | | | | |
+ + + + + +---+---+ +---+ +---+---+ +---+ + +
7 | | # | # # | | | | | | |
+---+ +---+---+---+---+ +---+ +---+ + +---+ +---+ +
6 | | # # | | | | | | | | |
+ +---+ +---+ +---+ + +---+ + +---+---+---+ + +
5 | | # # | | | | | |
+---+ +---+ +---+ +---+ +---+---+ + +---+ +---+ +
4 | | | # # | | | | | | | |
+ +---+ +---+ +---+ +---+ + + +---+---+ + +---+
3 | | | # | | | | | | |
+ +---+---+ + + +---+---+---+ +---+ + + +---+ +
2 | # # | | # | | | | | | |
+ + + +---+ + + +---+ +---+ +---+ + +---+---+
1 | # | # # # # | | |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
a b c d e f g h i j k l m n o p