TL;DR

On with TASK #2 from The Weekly Challenge #137. Enjoy!

# The challenge

You are given a number, 10 <= $n <= 1000. Write a script to find out if the given number is Lychrel number. To keep the task simple, we impose the following rules: a. Stop if the number of iterations reached 500. b. Stop if you end up with number >= 10_000_000.  According to wikipedia: A Lychrel number is a natural number that cannot form a palindrome through the iterative process of repeatedly reversing its digits and adding the resulting numbers. Example 1 Input:$n = 56
Output: 0

After 1 iteration, we found palindrome number.
56 + 65 = 121


Example 2

Input: $n = 57 Output: 0 After 2 iterations, we found palindrome number. 57 + 75 = 132 132 + 231 = 363  Example 3 Input:$n = 59
Output: 0

After 3 iterations, we found palindrome number.
59 +  95 =  154
154 + 451 =  605
605 + 506 = 1111


# The questions

The only real question is… what should we return if the number is suspected to be a Lycherel? I’ll return 1.

It’s interesting the limit at 500 iterations - I guess that with the other limit at 10 millions, it will never be hit.

# The solution

We’ll start with Perl here. The reverse function flips a string, and an integer in Perl has a dual-life as a string, so it basically works:

#!/usr/bin/env perl
use v5.24;
use warnings;
use experimental 'signatures';
no warnings 'experimental::signatures';

say maybe_lychrel(shift || 196);

sub maybe_lychrel ($n) { while ($n < 10_000_000) {
my $r = reverse$n;
return 0 if $n eq$r;
$n +=$r;
}
return 1;
}


In Raku it’s basically the same. We can have more input checks for free, of course:

#!/usr/bin/env raku
use v6;

sub MAIN (Int:D $x where 10 <= * <= 1000 = 196) { maybe-lychrel($x).put }

sub maybe-lychrel (Int:D $n is copy where * > 0) { while$n < 10000000 {
my $r =$n.flip;
return 0 if $n eq$r;
$n +=$r;
}
return 1;
}


This time the right sub/method is flip, because reverse is for listy stuff. Apart from this… it’s a copy.

Stay safe everybody!

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