Merge pull request 'Aufgabe2, Codewars Uebung Vigenère Cipher Helper kyu4' (#2) from Aufgabe2 into master

Reviewed-on: #2

src/Woche2/aufgabe2.py

@@ -0,0 +1,41 @@
+def key_string(key, text):
+    keystring = key
+    while len(keystring) <= len(text):
+        keystring += key
+    return keystring[: len(text)]
+
+
+class VigenereCipher(object):
+    def __init__(self, key, alphabet):
+        self.alphabet = alphabet
+        self.key = key
+        self.keymap = []
+        for i in range(len(alphabet)):
+            self.keymap.append(alphabet)
+            alphabet = alphabet[1:] + alphabet[0]
+
+    def encode(self, text):
+        keystring = key_string(self.key, text)
+        encode_string = ""
+
+        for index, i in enumerate(text):
+            index_alpha = self.alphabet.find(i)
+            if index_alpha == -1:
+                encode_string += i
+            else:
+                index_key = self.alphabet.find(keystring[index])
+                encode_string += self.keymap[index_key][index_alpha]
+        return encode_string
+
+    def decode(self, text):
+        keystring = key_string(self.key, text)
+        decode_string = ""
+
+        for index, i in enumerate(text):
+            if self.alphabet.find(i) == -1:
+                decode_string += i
+            else:
+                index_key = self.alphabet.find(keystring[index])
+                index_alpha = self.keymap[index_key].find(i)
+                decode_string += self.alphabet[index_alpha]
+        return decode_string