sicp exercise 2.62

;; Exercise 2.62.  Give a (n) implementation of union-set for sets represented as ordered lists.


(define (union-set set1 set2)
    (cond ((null? set1) set2)
          ((null? set2) set1)
          ((and (null? set1) (null? set2)) (list))
          (else
            (let ((x1 (car set1))
                 (x2 (car set2)))
              (cond ((> x1 x2) (cons x2
                                     (union-set set1 (cdr set2))))
                    ((= x1 x2) (cons x1
                                     (union-set (cdr set1) (cdr set2))))
                    ((< x1 x2) (cons x1
                                     (union-set (cdr set1) set2))))))))


(define set1 (list 100 200 300 400 500))
(define set2 (list 10 20 30 40 50))
(define set3 (list 1 2 35 45 55))
(define set4 (list 10 20 50 70 90))


(display (union-set set1 set2)) (newline)
(display (union-set set2 set3)) (newline)
(display (union-set set3 set4)) (newline)
(display (union-set set2 set4)) (newline)