Collatz Conjecture

[kanen]

I'm working on a New Lesson in Lisp this week and decided to tackle Collatz Conjecture.



I am going to express the code two ways. Firstly, as a 'standard' programming example and secondly as a Lisp programming example.



So, I thought I'd share the standard example and give the forums a chance to comment and optimize or convert to a more Lisp-y way of doing things.

Code Select Expand

;
; http://streamtech.nl/problemset/100.html
; aka http://en.wikipedia.org/wiki/Collatz_conjecture
;

(define (collatz)
   (println "Collatz Conjecture: low high (ENTER/RETURN to end)")
   (until (= (set 'p (read-line)) "")
      (set 'in (map int (parse p " ")) )
      (set 'low (in 0) 'high (in 1))
      (set 'max_count 0)
      (dolist (num (sequence low high))
         (set 'cnt 1)
         (while (!= num 1)
            (if (!= (mod num 2) 0)
               (set 'num (+ (* 3 num ) 1))
               (set 'num (/ num 2))
            )
            (inc cnt)
            (if (< max_count cnt) (setf max_count cnt))
         )
      )
      (println low " " high " " max_count)
   )
)

(collatz)

The results from this code are:



1 10

1 10 20

100 200

100 200 125

...