pushが結構便利。 ;;; ;; P09 (**) Pack consecutive duplicates of list elements into sub-lists. ;; If a list contains repeated elements they should be placed in separate ;; sub-lists. ;; ;; Example: ;; * (pack '(a a a a b c c a a d e e e e )…

(car nil) (cdr nil)がそれぞれnilを返すのを忘れててはまりました。 ;;; ;; P08 (**) Eliminate consecutive duplicates of list elements ;; If a list contains repeated elements they should be replaced with a single ;; copy of the elemnt. The ord…

consだったら再帰で木を下る。 結果はaccに溜めていって、最後にreverse。 ;;; ;; P07 (**) Flatten a nested list structure. ;; Transform a list, possibly holding lists as elemnts into a 'flat' list by ;; Replacing each list with its elements (r…

少し悩んだけど、簡単な方法で。 ;;; ;; P06 (*) Find out whether a list a palindrome. ;; A palindrome can be read forward or backward; e.g. (x a m a x) ;; Example: ;; * (palindrome-p '(a b c b a)) ;; t ;; * (palindrome-p '(a b c b)) ;; nil (…

;;; ;; P12 (**) Decode a run-length encoded list. ;; Given a run-length code list generated as specified in ;; problem P11. Construct its uncompressed version. (defun decode (lis) (let ((acc nil)) (dolist (elem lis) (cond ((atom elem) (pus…

;;; ;; P11 (*) Modified run-length encoding. ;; Modify the result of problem P10 in such a way that if an element ;; has no duplicates it is simply copied into the result list. ;; Only elements with duplicates are transferred as (N E) list…

P09の成果を使う。 ;;; ;; P10 (*) Run-length encoding of a list. ;; Use the result of problem P09 to implement the so-called run-length ;; encoding data compression method. Consecutive duplicates of elements ;; are encoded as lists (N E) wh…