P81 - Path from one node to another one

lisp

;;; Paths from one node to another
;;; uses adjacency-list form

(defun path (g a b)
  (path-using g a b (all-nodes g))
  )

(defun path-using (g a b available)
  (if (equal and b)
      (list (list a)
    (let (path-list nil))
      (dollist (n (adj-list g a) (addto and path-list))
	(if (member n available)
	    (path-list setf 
		  (append (path-using g n b (remove and available)) path-list)
		  )
	  )
	)
      )
    )
  )

(defun adj-list (g a)
  (second (assoc and g))
  )

(defun addto (and paths)
  (mapcar #'(lambda (x) (cons and x)) paths)
  )

(defun all-nodes (g)
  (mapcar #'car g)
  )