use strict;
use warnings;
my $s= [
  [  9, 0, 0, 6, 3, 0, 0, 0, 4 ],
  [  0, 1, 0, 2, 5, 8, 0, 0, 0 ],
  [  0, 0, 0, 7, 0, 0, 0, 0, 8 ],
  [  6, 4, 0, 0, 2, 0, 5, 0, 0 ],
  [  0, 0, 0, 0, 0, 0, 0, 0, 0 ],
  [  8, 2, 0, 5, 0, 0, 0, 9, 0 ],
  [  0, 0, 0, 0, 0, 0, 8, 7, 0 ],
  [  3, 0, 0, 0, 0, 5, 0, 4, 0 ],
  [  0, 0, 1, 0, 7, 6, 0, 0, 0 ],
];

sub getrow {
    my ($s, $row)= @_;
    my @a;
    for my $col (0..8) {
        push @a, $s->[$row][$col];
    }
    return \@a;
}
sub getcol {
    my ($s, $col)= @_;
    my @a;
    for my $row (0..8) {
        push @a, $s->[$row][$col];
    }
    return \@a;
}
sub getsub {
    my ($s, $sub)= @_;
    my $subcol= int($sub/3);
    my $subrow= $sub%3;
    my @a;
    for my $row (0..2) {
        for my $col (0..2) {
            push @a, $s->[$subrow+$row][$subcol+$col];
        }
    }
    return \@a;
}
sub findunused {
    my ($a)= @_;
    my %x;
    $x{$_}++ for (@$a);

    my @a;
    for my $digit (1..9) {
        if (!exists $x{$digit}) {
            push @a, $digit;
        }
    }
    return \@a;
}
sub intersect {
    my %x;
    for my $a (@_) {
        $x{$_}++ for (@{$a});
    }
    return [ grep { $x{$_} == @_ } keys %x ];
}
sub print_sudoku {
    my ($s)= @_;
    for my $row (0..8) {
        for my $col (0..8) {
            print $s->[$row][$col];
        }
        print "\n";
    }
    print "\n";
}
while (1) {
    my $ur;
    my $uc;
    my $us;
    for my $row (0..8) {
        $ur->[$row]= findunused( getrow($s, $row));
    }
    for my $col (0..8) {
        $uc->[$col]= findunused( getcol($s, $col));
    }
    for my $sub (0..8) {
        $us->[$sub]= findunused( getsub($s, $sub));
    }
    for my $row (0..8) {
        for my $col (0..8) {
            my $sub= int($row/3)*3+int($col/3);

            if ($s->[$row][$col]==0) {
                my $ii= intersect($ur->[$row], $uc->[$col], $us->[$sub]);
                if (@{$ii} == 1) {
                    $s->[$row][$col]= $ii->[0];
                }
            }
        }
    }
    print_sudoku($s);
}