challenge 331: fix task2 solutions

3 files changed, 77 insertions, 10 deletions

diff --git a/challenge-331/ysth/go/ch-2.go b/challenge-331/ysth/go/ch-2.go
index 421c5a8892..dc35146668 100644
--- a/challenge-331/ysth/go/ch-2.go
+++ b/challenge-331/ysth/go/ch-2.go
@@ -6,18 +6,33 @@ import (
 )
 
 func buddy_strings(string1 string, string2 string) bool {
-    if (string1 == string2) { return false }
     var runes1 = []rune(string1)
     var runes2 = []rune(string2)
     if len(runes1) != len(runes2) { return false }
-    var differences int = 0
+    var swaps int = 0
+    var pair_exists bool = false
+    var previous_character1 rune
+    var previous_character2 rune
     for i := range runes1 {
-        if runes1[i] != runes2[i] {
-            differences++
-            if differences > 1 { return false }
+        var character1 rune = runes1[i]
+        var character2 rune = runes2[i]
+        if swaps == 1 {
+            // second character of swap
+            if previous_character2 != character1 || character2 != previous_character1 {
+                return false
+            }
+            swaps = 2
+        } else if character1 != character2 {
+            // starting the first swap
+            if swaps > 0 { return false }
+            previous_character1 = character1
+            previous_character2 = character2
+            swaps = 1
         }
+        pair_exists = pair_exists || i > 0 && runes1[i-1] == runes1[i]
     }
-    return true 
+
+    return swaps == 0 && pair_exists || swaps == 2
 }
 
 func main() {
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() {
diff --git a/challenge-331/ysth/python/ch-2.py b/challenge-331/ysth/python/ch-2.py
index 6d0f7c80e4..a87815fd24 100644
--- a/challenge-331/ysth/python/ch-2.py
+++ b/challenge-331/ysth/python/ch-2.py
@@ -3,7 +3,30 @@ import regex
 from itertools import batched
 
 def buddy_strings(string1: str, string2: str) -> bool:
-    return True if regex.fullmatch(regex.escape(string1)+'{1<=s<=1}', string2) else False
+    if len(string1) != len(string2):
+        return False
+    swaps = 0
+    pair_exists: bool = False
+    previous_character1: str
+    previous_character2: str
+    for i in range(len(string1)):
+        character1: str = string1[i]
+        character2: str = string2[i]
+        if swaps == 1:
+            # second character of swap
+            if previous_character2 != character1 or character2 != previous_character1:
+                return False
+            swaps = 2
+        elif string1[i] != string2[i]:
+            # starting the first swap
+            if swaps > 0:
+                return False
+            previous_character1 = character1
+            previous_character2 = character2
+            swaps = 1
+        pair_exists = pair_exists or i > 0 and string1[i-1] == string1[i]
+
+    return pair_exists and swaps == 0 or swaps == 2
 
 def main() -> None:
     inputs: list[str] = sys.argv[1:]