# FarmerWolfGoatCabbage

Skillnad (från version 3 till rådande version)

Sammanfattning: Rollback to 2008-09-05 00:16 UTC

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Known problem solved in elisp.

Here is little description. We have 2 banks (east and west). On the west bank we have farmer, wolf, goat, cabbage and one boat that can hold one or a couple of them, also if wolf stays with goat without farmer then wolf eats goat and if goat stays with cabbage without farmer then goat eats cabbage. Goal: cross a river without losses.

Try to fully understand what is going on!

```(defun fs (state) (nth 0 state))
(defun ws (state) (nth 1 state))
(defun gs (state) (nth 2 state))
(defun cs (state) (nth 3 state))

(defun op (els)
(cond ((equal els "w") "e")
((equal els "e") "w")))

(defun safe (state)
(cond ((and (not (equal (fs state) (gs state)))
(or (equal (ws state) (gs state))
(equal (gs state) (cs state)))) nil)
(t state)))

(defun make-state (f w g c)
(list f w g c))

(defun fw (state)
(cond ((equal (fs state) (ws state))
(safe (list (op (fs state))
(op (ws state))
(gs state)
(cs state))))
(t nil)))

(defun fg (state)
(cond ((equal (fs state) (gs state))
(safe (list (op (fs state))
(ws state)
(op (gs state))
(cs state))))
(t nil)))

(defun fc (state)
(cond ((equal (fs state) (cs state))
(safe (list (op (fs state))
(ws state)
(gs state)
(op (cs state)))))
(t nil)))

(defun ff (state)
(safe (list (op (fs state))
(ws state)
(gs state)
(cs state))))

(defun fpath (firth-s goal-s beenl)
(cond ((null firth-s) nil)
((equal firth-s goal-s) (reverse (cons firth-s beenl)))
((not (in firth-s beenl))
(or (fpath (ff firth-s) goal-s (cons firth-s beenl))
(fpath (fw firth-s) goal-s (cons firth-s beenl))
(fpath (fg firth-s) goal-s (cons firth-s beenl))
(fpath (fc firth-s) goal-s (cons firth-s beenl))))))

(defun in (elem list)
(cond ((null list) nil)
((equal elem (car list)) t)
(t (in elem (cdr list)))))

(fpath '("w" "w" "w" "w") '("e" "e" "e" "e") nil)
```