2 approaches by calculating the string of modulo distances of two neighboring digits
Any sequence of consecutive 1 or 9 reflects ascending or descending sequences.
The difficulty is to get all overlapping pairs in an elegant way w/o trouble with edge cases.
Version 1 manipulates pos() of m//g
Version 2 uses reduce {...;$b}
use List::Util qw/max reduce/;
while(<DATA>){
chomp;
#-- Version 1
my $diff="";
while (/(\d)(\d)/g) {
$diff.=($2-$1)%10;
pos($_)--;
}
my $v1= 1 + max map { length } $diff =~ m/(1+|9+)/g;
#--- Version 2
$diff="";
reduce { $diff.=($a-$b)%10; $b} split //;
my $v2= 1 + max map { length } $diff =~ m/(1+|9+)/g;
print "V1: $v1 V2: $v2 $_\n";
}
__DATA__
461771621368210983721913243963580233112903255149955120374576
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