CODEWITHSUNDEEP
listschemeequalsverification
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Reputation: 780

Scheme : Compare/Check if 2 lists are equal

I am looking for a function that compares or checks if 2 lists are equal.

It should ignore number order and duplicated numbers...

I already created a function that checks if a element is part of a list on another block, but I am having some problems with this one now.

Here's what I have

(define (ispart? x b)
      (cond ((null? b) #f)
            ((= x (car b)) #t)
             (else (ispart? x (cdr b)))))

    (define (check=? c1 c2)


(define (verification-1 c1 c2) 
        (cond((null? c1) 
            #t)
        ((ispart? (car c1) c2) (check=? (cdr c1) c2))))
   (define (verification-2 c1 c2) 
    (cond((null? c2) 
        #t)
  ((ispart? (car c2) c1) (check=? c1 (cdr c2)))))
    (if (equal? (and verification-1 verification-2) #t)
        #t
  (#f)))

I'm having problems with the conditions mainly, I am creating a check for each element of the first list to see if it belongs to the second list and then a check for each element of the second list. If any element fails that check then the lists are different.

I also tried this one but it doesn't ignore duplicated numbers or number order, so (3 2 1) is different from (1 2 2 3) and I don't want that to happen

    (define (lists=? lst1 lst2)
  (cond ((null? lst1) (null? lst2))
        ((null? lst2) #f)
        ((= (car lst1) (car lst2))
         (lists=? (cdr lst1) (cdr lst2)))
        (else #f)))

Upvotes: 1

Views: 5773

Answers (1)

amindfv
amindfv

Reputation: 8448

Given a function all, which says if all elements of a list are true, 

(define (all l)
   (cond ((null? l) #t)
         ((equal? #f (car l)) #f)
         (else (all (cdr l)))))

and given your ispart? function,

You can simply see if every element in the first list passes the ispart? test in the second list, and vice-versa: 

(define (set_equal l0 l1)
   (and (all (map (lambda (x) (ispart? x l1))
                  l0))
        (all (map (lambda (x) (ispart? x l0))
                  l1))))

Upvotes: 2

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