Course of Raku / Addendum 🆕 / Working with data / Numbers and mathematics / Exercises / Collatz steps

Solution: Collatz steps

Here is a possible solution to the task.

Code

my $n = 27;
my $steps = 0;

while $n != 1 {
    $n = $n %% 2 ?? $n div 2 !! 3 * $n + 1;
    $steps++;
}

say $steps;

🦋 You can find the source code in the file collatz.raku.

Output

111

Comments

1. The ternary ?? !! chooses the next value in one expression: halve $n when it is even ($n %% 2), otherwise apply 3 * $n + 1.

2. 27 is a famous small case that takes a surprisingly long detour — 111 steps — before it finally settles at 1.

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