; function to provide inut-output - reads the file
; data from the fine cities.dat
; global variables are start with *
; function tsp takes as an argument the list and solves the TSP problem

(defun skel1 ()
  (let (data_file sym_list)
    (setq data_file  (open "cities.dat" :direction :input))
    (setq *print_max* 30)
    
    (loop  
       (if (null (setq sym_list  (read data_file nil nil ))) (return))
       (solve_tsp sym_list)
    )
    (close data_file)
    '****Finished****
  )
)


; Here is a dummy version of tsp fuction which you will be required 
; to modify

(defun solve_tsp (sym_list)
  (setq *city_max* (length sym_list))

  (format t "~%Generating tours for following ~D cities:  ~%"  *city_max*)

  (dolist (item sym_list)
    (format t " ~A~%" item)
    )

  (setq *tour_cnt* 0)
  (permute sym_list  '())
 
  (format t "~% Tour count: ~D~%~%" *tour_cnt*)
)

; Function permute is invoked with two arguments 
; unused symbols and partial permutation (which is at the beginning null)
; the unused symbols are added to the front of the patial permutation list
; creating a child node, and permute is called recursively do generate 
; the grand children etc.

(defun permute (unused perm)
 (let ()
   (cond 
         ((null unused)
	  (cond 
	               ( (< *tour_cnt*  *print_max*) (print perm) )
                       ( (= *tour_cnt*  *print_max*) 
                         (format t "~%      supressing printing ...") )
                       )
          (setq *tour_cnt*  (+ *tour_cnt* 1))
	  )
         (t  (dolist (item unused)
	       (permute (remove item unused) (cons item perm))
                ))
   )
  )
)