Optimize cipher functions: fix O(n²) string concat and Vigenère keyword indexing

.gitignore

@@ -0,0 +1,69 @@
+# Byte-compiled / optimized / DLL files
+__pycache__/
+*.py[cod]
+*$py.class
+
+# C extensions
+*.so
+
+# Distribution / packaging
+.Python
+build/
+develop-eggs/
+dist/
+downloads/
+eggs/
+.eggs/
+lib/
+lib64/
+parts/
+sdist/
+var/
+wheels/
+*.egg-info/
+.installed.cfg
+*.egg
+
+# PyInstaller
+*.manifest
+*.spec
+
+# Installer logs
+pip-log.txt
+pip-delete-this-directory.txt
+
+# Unit test / coverage reports
+htmlcov/
+.tox/
+.coverage
+.coverage.*
+.cache
+nosetests.xml
+coverage.xml
+*.cover
+.hypothesis/
+.pytest_cache/
+
+# Translations
+*.mo
+*.pot
+
+# Environments
+.env
+.venv
+env/
+venv/
+ENV/
+env.bak/
+venv.bak/
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+*~
+
+# OS files
+.DS_Store
+Thumbs.db

decoders_AI_for_frontend.py

@@ -43,24 +43,26 @@ def url_decoder(data):
         return f" Error: {e}"
 
 def caesar_cipher(data, shift):
-    result = ""
+    result = []
     for char in data:
         if char.isalpha():
             base = ord("A") if char.isupper() else ord("a")
-            result += chr((ord(char) - base + shift) % 26 + base)
+            result.append(chr((ord(char) - base + shift) % 26 + base))
         else:
-            result += char
-    return result
+            result.append(char)
+    return ''.join(result)
 
 def vigenere_encoder(keyword, data):
     result = []
     keyword = keyword.lower()
     k_len = len(keyword)
-    for i, char in enumerate(data):
+    k_idx = 0
+    for char in data:
         if char.isalpha():
             base = ord('A') if char.isupper() else ord('a')
-            shift = ord(keyword[i % k_len]) - ord('a')
+            shift = ord(keyword[k_idx % k_len]) - ord('a')
             result.append(chr((ord(char) - base + shift) % 26 + base))
+            k_idx += 1
         else:
             result.append(char)
     return ''.join(result)
@@ -69,11 +71,13 @@ def vigenere_decoder(data, keyword):
     result = []
     keyword = keyword.lower()
     k_len = len(keyword)
-    for i, char in enumerate(data):
+    k_idx = 0
+    for char in data:
         if char.isalpha():
             base = ord('A') if char.isupper() else ord('a')
-            shift = ord(keyword[i % k_len]) - ord('a')
+            shift = ord(keyword[k_idx % k_len]) - ord('a')
             result.append(chr((ord(char) - base - shift) % 26 + base))
+            k_idx += 1
         else:
             result.append(char)
     return ''.join(result)