Factors of an integer: Difference between revisions

=={{header|LFE}}==

===Using List Comprehensions===

This following function is elegant looking and concise. However, it will not handle large numbers well: it will consume a great deal of memory (on one large number, the function consumed 4.3GB of memory on my desktop machine):

<lang lisp>

(defun factors (n)

(list-comp

((<- i (when (== 0 (rem n i))) (lists:seq 1 (trunc (/ n 2)))))

i))

</lang>

===Non-Stack-Consuming===

This version will not consume the stack (this function only used 18MB of memory on my machine with a ridiculously large number):

<lang lisp>

(defun factors (n)

"Tail-recursive prime factors function."

(factors n 2 '()))

(defun factors

((1 _ acc) acc)

((n _ acc) (when (=< n 0))

#(error undefined))

((n k acc) (when (== 0 (rem n k)))

(factors (div n k) k (cons k acc)))

((n k acc)

(factors n (+ k 1) acc)))

</lang>

Output in the REPL:

<lang lisp>

> (factors 10677106534462215678539721403561279)

(104729 104729 104729 98731 98731 32579 29269)

</lang>