Perl Sudoku solver

sudoku.pl

#!/usr/bin/perl

# usage: $0 00030050204050205040520370782340520508485019857294857049587

use integer;
@A = split //, <>;

sub R {
    return if grep {             # if this solution is invalid, bail
             ($_ / 9 == $i / 9   # find pairs of boxes to compare
               || $_ % 9 == $i % 9
               || $_ / 27 == $i / 27 && $_ % 9 / 3 == $i % 9 / 3)
             && $_!=$i && $A[$i] && $A[$_]==$A[$i] } 0 .. 80;
print @A;                        # debug
    $i++ while $A[$i];           # save this the child calls
    my$x=$i;
    die @A if $i>80;              # out of bounds
    R( $A[$i=$x] = $_ ) for 1..9; # recurse on each possible choice
    $A[$x]=0;
   # return $i=$x;
}
R