CODEWITHSUNDEEP
schemetail-recursion
n00b
n00b

Reputation: 3

Scheme. Tail recursive?

any tail-recursive version for the below mentioned pseudocode ? Thanks !

(define (min list)
  (cond 
   ((null? list) '())
   ((null? (cdr list)) (car list))
   (#t (let ((a (car list))
             (b (min (cdr list))))
         (if (< b a) b a)))))

Upvotes: 0

Views: 1310

Answers (5)

Vijay Mathew
Vijay Mathew

Reputation: 27164

(define (min list)
   (min-helper list #f))

(define (min-helper list min-so-far)
   (if (null? list) 
       min-so-far
       (let ((m (car list)))
            (if (eq? min-so-far #f)
                (set! min-so-far m))
            (if (< m min-so-far)
                (min-helper (cdr list) m)
                (min-helper (cdr list) min-so-far)))))

Upvotes: 0

George Kangas
George Kangas

Reputation: 1

(define (min ns)
  (let loop ( (ns-left ns) (min-so-far maxint) )
    (if (null? ns-left)
      min-so-far
      (loop
        (cdr ns-left)
        (if (< (car ns-left) min-so-far)
          (car ns-left)
          min-so-far )))))

Upvotes: 0

SK-logic
SK-logic

Reputation: 9714

 (define (min list)
  (let imin ((l (cdr list))
         (m (car list)))
    (cond
     ((null? l) m)
     (else
      (let ((a (car l)))
        (imin (cdr l)
              (if (< a m) a m)))))))

Upvotes: 1

Aidan Cully
Aidan Cully

Reputation: 5507

You should read up on the fold higher-order functions.

Upvotes: 2

sepp2k
sepp2k

Reputation: 370102

Define a helper function that takes a list and the smallest element found so far (let's call it b). If the list is empty, it should return b, otherwise if the head of the list (a) is smaller than b than it should return (helper (cdr list) a), otherwise (helper (cdr list) b). Now we can define (min list) as (helper (cdr list) (car list)).

Upvotes: 1

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