Cycle detection: Difference between revisions

=={{header|Factor}}==

This is a strict translation of the Python code from the Wikipedia article. Perhaps a more idiomatic version could be added in the future, although there is value in showing how Factor's lexical variables differ from most languages. A variable binding with <code>!</code> at the end is mutable, and subsequent uses of that name followed by <code>!</code> change the value of the variable to the value at the top of the data stack.

<lang factor>USING: formatting kernel locals make math prettyprint ;

: cyclical-function ( n -- m ) dup * 1 + 255 mod ;

:: brent ( x0 quot -- λ μ )

1 dup :> ( power! λ! )

x0 :> tortoise!

x0 quot call :> hare!

[ tortoise hare = not ] [

power λ = [

hare tortoise!

power 2 * power!

0 λ!

] when

hare quot call hare!

λ 1 + λ!

] while

0 :> μ!

x0 dup tortoise! hare!

λ [ hare quot call hare! ] times

[ tortoise hare = not ] [

tortoise quot call tortoise!

hare quot call hare!

μ 1 + μ!

] while

λ μ ; inline

3 [ 20 [ dup , cyclical-function ] times ] { } make nip .

3 [ cyclical-function ] brent

"Cycle length: %d\nCycle start: %d\n" printf</lang>

{{out}}

<pre>

{ 3 10 101 2 5 26 167 95 101 2 5 26 167 95 101 2 5 26 167 95 }

Cycle length: 6

Cycle start: 2

</pre>