#lang sicp

; element-of-set? is the exact same
; O(n)
(define (element-of-set? x set)
  (cond ((null? set) false)
	((equal? x (car set)) true)
	(else (element-of-set? x (cdr set)))))

; O(1)
(define (adjoin-set x set)
  (cons x set)) ; we don't have to check anymore

; O(n), where n is the length of set1
(define (union-set set1 set2)
  (append set1 set2))

; intersection-set can still be the exact same
; O(n^2)
(define (intersection-set set1 set2)
  (cond ((or (null? set1) (null? set2)) '())
	((element-of-set? (car set1) set2)
	 (cons (car set1) (intersection-set (cdr set1) set2)))
	(else (intersection-set (cdr set1) set2))))