09/07/21 12:32:04
>>523
(define (nodenum t)
(cond ((not (pair? t)) 0)
((or (not (pair? (cdr t))) (not (pair? (cddr t)))) "error:not a binary tree")
(else (+ 1 (nodenum (cadr t)) (nodenum (caddr t))))))
(nodenum '(1 leaf leaf)) ;1
(nodenum '(1 'leaf)) ;error
(nodenum '(1 (2 leaf leaf) (3 leaf (4 leaf leaf)))) ;4