challenge 331: fix task2 solutions

1 files changed, 32 insertions, 3 deletions

diff --git a/challenge-331/ysth/perl/ch-2.pl b/challenge-331/ysth/perl/ch-2.pl
index 2aebf3e46f..f183cd768c 100644
--- a/challenge-331/ysth/perl/ch-2.pl
+++ b/challenge-331/ysth/perl/ch-2.pl
@@ -1,11 +1,40 @@
 use 5.040;
 
 use utf8::all; # utf8 @ARGV
-use Text::Fuzzy ();
+
+# replacement for the pre-perl5.28 stringwise xor that worked on any codepoints (up to uvsize)
+sub bitwise_xor {
+    # copy/stringize arguments so overload/magic only happens once per arg
+    my $a = "$_[0]";
+    my $b = "$_[1]";
+    if (!utf8::is_utf8($a) && !utf8::is_utf8($b)) {
+        no if $] > 5.022, 'feature' => 'bitwise';
+        return $a ^ $b;
+    }
+    if (length $a < length $b) {
+        $a =~ s/./chr(ord $& ^ ord($b =~ m!.!gs && $&))/gse;
+        return $a . substr $b, length $a;
+    }
+    else {
+        $b =~ s/./chr(ord $& ^ ord($a =~ m!.!gs && $&))/gse;
+        return $b . substr $a, length $b;
+    }
+}
 
 sub buddy_strings($string1, $string2) {
-    length $string1 == length $string2
-        and Text::Fuzzy->new($string1, max => 1, no_exact => 1) == 1
+    if ($string1 eq $string2) {
+        # a doubled character to "swap"
+        return $string1 =~ /(.)\1/s;
+    }
+    else {
+        return
+            # lengths must match
+            length $string1 == length $string2
+            # exactly 2 differing characters, adjacent
+            && bitwise_xor($string1, $string2) =~ /^\0*([^\0])\1\0*\z/
+            # in opposite order in the two strings
+            && substr($string1, $-[1], 2) eq reverse substr($string2, $-[1], 2)
+    }
 }
 
 sub main() {