sicp每日一题[2.59]
Exercise 2.59
Implement the union-set operation for the unordered-list representation of sets.
这道题很简单，仿照 intersection-set 稍作修改就可以实现了
(define (union-set set1 set2)
(cond ((null? set1) set2)
((element-of-set? (car set1) set2)
(union-set (cdr set1) set2))
(else (cons (car set1) (union-set (cdr set1) set2)))))
(define set1 (list 1 3 5 'a 'b 'c))
(define set2 (list 2 4 6 'a 'd 'c))
(union-set set1 set2)
; 执行结果
'(1 3 5 b 2 4 6 a d c)