Question

Who can help me with a code that returns the difference the difference in two different lists i.e the set in A and not in B. like (set-difference ‘(1 2 4 5 6) ‘(4 5 6 2 8) is 1. This is was an in-class lab assessment and I wanted to know it would had been done. I know it deals with the aspect of linear time, but I don’t really know how to implement that in scheme.

Answer 1

Try this:

(define (set-difference s1 s2)
  (cond ((null? s1)
         '())
        ((not (member (car s1) s2))
         (cons (car s1) (set-difference (cdr s1) s2)))
        (else
         (set-difference (cdr s1) s2))))