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";
}

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