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This may get me a very clever, -10, but I've tweaked the program to run rather quickly (-n 22 runs in a few seconds) by using a known general solution as the basis of my regex. Technically, it still generates a regular expression and matches it against the who-doesn't-attack-whom string, so -n 3 returns no match.

#!/usr/bin/perl use strict; use warnings 'all'; use Getopt::Long; Getopt::Long::Configure ("bundling"); GetOptions ('p|print' => \my $print, 'P|Print' => \my $Print, 'n|number=i' => \(my $nr_of_queens = 8) ); my @rows = 1 .. $nr_of_queens; my @cols = ('a' .. 'z') [0 .. $nr_of_queens - 1]; sub a2i {ord ($_ [0]) - ord ('a') + 1} sub i2a {chr ($_ [0] + ord ('a') - 1)} # Given a square, return all non-attacked squares on columns to # the *left* of the given square. (a1 is the lower left corner). sub free { my ($C, $R) = $_ [0] =~ /(\D)(\d+)/; $C = a2i $C; map {join "" => i2a ($_ -> [0]), $_ -> [1]} grep {$_ -> [0] != $C && $_ -> [1] != $R && abs ($_ -> [0] - $C) != abs ($_ -> [1] - $R)} map {my $c = a2i $_; map {[$c, $_]} @rows} @cols [0 .. $C - 1] } my ($str, $re) = ('', ''); my $solrow = 0; foreach my $c (@cols) { $str .= ";," . (join "," => map {"$c$_"} @rows) . ",\n"; $solrow += 2; $solrow = 1 if $solrow > $nr_of_queens; $re .= ".*\n" unless $c eq 'a'; $re .= ";.*,($c$solrow),"; next if $c eq 'a'; $re .= sprintf "(?:.*\n){%d}\\%d:", $solrow, a2i($c); for my $i (1..a2i($c)-1) { $re .= ".*,\\$i,"; } $re .= sprintf "(?:.*\n){%d}", $nr_of_queens - $solrow; map {$str .= "$_:," . join (",," => free ($_)) . ",\n"} map {"$c$_ +"} @rows; } if ($print || $Print) { print "'$str' =~ \n/^$re/\n"; exit if $Print; } if (my @a = $str =~ /^$re/) { print "[@a]\n"; } __END__

In reply to Re: The N-queens problem using pure regexes by Roy Johnson
in thread The N-queens problem using pure regexes by Abigail-II

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