一日空いてしまったので復習から。

問題解答

問2.68

(define (encode-symbol symbol tree)
  (define (it symbol tree code)
    (cond ((null? symbol) '())
          ((leaf? tree) code)
          ((element-of-set? symbol (symbols (left-branch tree)))
           (it symbol (left-branch tree) (append code '(0))))
          ((element-of-set? symbol (symbols (right-branch tree)))
           (it symbol (right-branch tree) (append code '(1))))
          (else (error "bad symbol" symbol))))

  (it symbol tree '()))

(define (encode message tree)
  (if (null? message)
      '()
      (append (encode-symbol (car message) tree)
              (encode (cdr message) tree))))

(encode '(A D A B B C A) sample-tree)

答えはでたけど何かコードが汚い。