程序设计方法14.2.1

判断一个数是否在树中出现.ss

;;contains-bt
;;二叉搜索树
(define (contains-bt num bt)
  (cond 
    [(empty? bt) false]
    [else (cond 
           [(= (node-ssn bt) num) true]
           [(contains-bt num (node-left bt))true]
           [(contains-bt num (node-right bt))true]
           [else false]
            )]
    ))
(define-struct node (ssn name left right))
(define bt (make-node 15 'd (make-node 10 'a empty empty) (make-node 24 'c  empty empty)))
(contains-bt 120 bt)