http://qs321.pair.com?node_id=418794

in reply to Comparison by position and value

Update: I didn't read closely enough. This doesn't account for the case where the same digit appears in different positions in each sequence -- i.e., I'm only comparing each individual position.

Update 2: Here's a more complicated version that accounts for what I missed, the assumption still being that a given digit can only appear once in a sequence.

```sub compatible
{
my (\$s1, \$s2) = @_;
my %hashed;
my \$diff = 0;

my (\$one, \$two);
my @counts;
my \$n = 10;

#
# Hash so that each \$s1 value is a key with its corresponding
# \$s2 value as the hashed value.
#
@hashed{map {(\$_ eq '_') ? \$n++ : \$_} split("", \$s1)} =
map {(\$_ eq '_') ? \$n++ : \$_} split("", \$s2);

#
# Compare each \$s1->\$s2 pair
#
while ((\$one, \$two) = each %hashed)
{
next if (\$one == \$two);

last if ((\$diff = (++\$counts[\$one] - 1)) > 0);
last if ((\$diff = (++\$counts[\$two] - 1)) > 0);

\$diff = 0;
next if ( (\$one >= 10) || (\$two >= 10) );

last if ((\$diff = (\$one - \$two)) != 0);
}

print "\$s1\n\$s2\n", (\$diff == 0) ? "compatible" : "incompatible",
+"\n\n";
}
Revised output:
```_8__3__19
48____7__
compatible

_8__3__19
4_2___7__
compatible

_8__3__19
4_8___7__
incompatible

__8_3__19
48____7__
incompatible

__8_3__19
84____7__
incompatible

_8__3__19
48_____7_
incompatible

I'm not sure how fast this is compared to the other methods, but here's a way to do it using a hash and a short circuited loop comparison of each hashed key/value:

```use strict;

sub compatible
{
my (\$s1, \$s2) = @_;
my %hashed;
my \$diff = 0;
my (\$one, \$two);

#
# Hash so that each \$s1 value is a key with its corresponding
# \$s2 value as the hashed value.
#
@hashed{split("", \$s1)} = split("", \$s2);

#
# Compare each \$s1->\$s2 pair
#
while ((\$one, \$two) = each %hashed)
{
next if ( (\$one eq '_') || (\$two eq '_') );
last if ((\$diff = (\$one - \$two)) != 0);
}

print "\$s1\n\$s2\n", (\$diff == 0) ? "compatible" : "incompatible",
+"\n\n";
}

my @tests =
(qw/
_8__3__19
48____7__

_8__3__19
4_2___7__

_8__3__19
4_8___7__

__8_3__19
48____7__

__8_3__19
84____7__

_8__3__19
48_____7_
/
);

my (\$s1, \$s2);
while (defined(\$s1 = shift(@tests)))
{
\$s2 = shift(@tests);
compatible(\$s1, \$s2);
}
Output:
```_8__3__19
48____7__
compatible

_8__3__19
4_2___7__
compatible

_8__3__19
4_8___7__
compatible

__8_3__19
48____7__
compatible

__8_3__19
84____7__
compatible

_8__3__19
48_____7_
incompatible