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#!/usr/bin/perl
use warnings;
use strict;
use feature qw{ say };
use constant SUM => 15;
sub still_valid {
my ($matrix) = @_;
COORD:
for my $coords ([0, 1, 2], [3, 4, 5], [6, 7, 8], [0, 3, 6],
[1, 4, 7], [2, 5, 8], [0, 4, 8], [2, 4, 6]) {
$matrix->[$_] or next COORD for @$coords;
return unless SUM == $matrix->[ $coords->[0] ]
+ $matrix->[ $coords->[1] ]
+ $matrix->[ $coords->[2] ];
}
return 1
}
{ my @solutions;
sub fill {
my ($matrix, @unused) = @_;
unless (@unused) {
push @solutions, [@$matrix];
return
}
my $i = 0;
++$i until $i > $#$matrix || $matrix->[$i] == 0;
for my $u (0 .. $#unused) {
$matrix->[$i] = $unused[$u];
fill($matrix, @unused[0 .. $u - 1, $u + 1 .. $#unused])
if still_valid($matrix);
}
$matrix->[$i] = 0;
}
sub magical_matrix {
fill([(0) x 9], 1 .. 9);
return @solutions
}
}
my @s = magical_matrix();
for my $m (@s) {
say "@$m[0, 1, 2]";
say "@$m[3, 4, 5]";
say "@$m[6, 7, 8]";
say "---";
}
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