Category: | Cryptography | |||
Author/Contact Info | Randal L. Schwartz, merlyn | |||
Description: | Usage: pat ABCABC finds any word that has three repeated characters twice in a row (such as "murmur" in my dictionary). pat XYYX finds words that are four-character palindromes, such as "deed". In the result, X and Y must be different.
So pat ABCDEFGHAB finds ten-letter words whose first two and last
two characters are identical, but the remaining letters are all distinct, such
as "thousandth" or "Englishmen".
To require literal characters, use lowercase, as in pat fXXd, requiring an f, two identical letters, and a d, such as "food" or "feed". For grins, dumps the regex that the pattern has been transformed into, so you can write your own, or see how much work you're avoiding by using this program.
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#!/usr/bin/perl -w use strict; open WORDS, "/usr/dict/words" or die "no more words: $!"; for (@ARGV) { my @avoid = do { my @lits = /[a-z]/g; @lits ? "[" . join("", @lits) . "]" : () }; my %template; my $regex = "^"; for (split //) { if (/[a-z]/) { $regex .= "$_"; } elsif (/[A-Z]/) { if (exists $template{$_}) { $regex .= $template{$_}; } else { my $id = 1 + keys %template; if (@avoid) { $regex .= "(?!" . join("|", @avoid) . ")"; } $regex .= "(.)"; push @avoid, $template{$_} = "\\$id"; } } else { warn "ignoring $_"; } } $regex .= "\$"; print "$_ => $regex\n"; seek WORDS, 0, 0; while (<WORDS>) { next unless /$regex/i; print; } } |
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