Weekly Challenge #082 Task #1 :: (Raku)

TASK #1 › Common Factors

Submitted by: Niels van Dijke

You are given 2 positive numbers $M and $N.

Write a script to list all common factors of the given numbers.
Example 1:

Input:
    $M = 12
    $N = 18

Output:
    (1, 2, 3, 6)

Explanation:
    Factors of 12: 1, 2, 3, 4, 6
    Factors of 18: 1, 2, 3, 6, 9

Example 2:

Input:
    $M = 18
    $N = 23

Output:
    (1)

Explanation:
    Factors of 18: 1, 2, 3, 6, 9
    Factors of 23: 1

It was really easy than I think it should be... quite opposite to Task #2 which I think easier.

If we are given N = 1000, We can get a series of divisors like below

> [ 1 .. 1000 ].grep({ 1000 %% $_ })
(1 2 4 5 8 10 20 25 40 50 100 125 200 250 500 1000)

we can use for loop, or "gather and take" if you want.

if we are done with finding both divisors we can create a
set which contains intersection by

> [ 1 .. 12 ].grep({ 12 %% $_ }) (&) [ 1..18 ].grep({ 18 %% $_ })
Set(1 2 3 6)

and only grab the values

([ 1 .. 12 ].grep({ 12 %% $_ }) (&) [ 1..18 ].grep({ 18 %% $_ })).keys.sort
(1 2 3 6)

infix (&), infix ∩
I used "∩" infix during the Challenge #076 Task #2 as you can see in this code.
I wrote something like this perl code in Raku. but couldn't see big difference or slightly faster when using "Set".😅 so I thought "why should I use my own code if raku gives me faster one?", and changed it into simple line. quite convenient operators!!

gcd Infix

But we have gcd in Raku, so we don't have to make both divisors.

with [gcd] (12,18) { [ 1..$_ ].grep(-> \k { $_ %% k }) }
(1 2 3 6)

Final Code

sub MAIN ( *@n where { @n.elems == 2 and @n.all ~~ Int and @n.all > 0 } ) {
    with [gcd] @n {
        say( [1.. $_].grep(-> \k {$_ %% k}));
    }
}

If we are still unsure, we can still use "any"

sub MAIN ( *@n where { @n.elems == 2 and @n.all ~~ Int and @n.all > 0 } ) {
    say( [1.. @n.min].grep({any(@n)%%$_}) );
}

Thank you for reading ~!