Longest palindromic substrings: Difference between revisions

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=={{header|Perl}}==

The short one - find all palindromes with one regex.

<syntaxhighlight lang="perl">~~#!/usr/bin/perl~~

<syntaxhighlight lang="perl">use strict;

use strict; # https://rosettacode.org/wiki/Longest_palindromic_substrings

use warnings;

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Longest Palindrome For abaracadabra = aba ara aca ada

</pre>

The faster one - does the million digits of Pi in under half a second.

<syntaxhighlight lang="perl">~~#!/usr/bin/perl~~

The faster one - does the million digits of Pi in under half a second.

use strict; # https://rosettacode.org/wiki/Longest_palindromic_substrings

<syntaxhighlight lang="perl">use strict;

use warnings;

use feature 'bitwise';

#@ARGV = 'pi.dat'; # uncomment to use this file or add filename to command line

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my $right = substr $forward, $i, $range;

my $left = substr $backward, $length - $i, $range;

( $right ^ $left ) =~ /^\0\0+/ and # evens

( $right ^. $left ) =~ /^\0\0+/ and # evens

($len = 2 * length $&) >= $#best and

$best[ $len ]{substr $forward, $i - length $&, $len}++;

( $right ^ "\0" . $left ) =~ /^.(\0+)/ and # odds

( $right ^. "\0" . $left ) =~ /^.(\0+)/ and # odds

($len = 1 + 2 * length $1) >= $#best and

$best[ $len ]{substr $forward, $i - length $1, $len}++;