Merge pull request 'Aufgabe 3 Codewars' (#4) from Aufgabe3 into master

Reviewed-on: #4

Code sieht soqweit solide aus. Kleine Anmerkung zu den Kommentaren: Wenn Du die anstelle mit # oberhalb der Funktion mit """ innerhalb der Funktion schreibst, kannst Du die für automatische Dokumentierungen (z.B. sphinx) und für help() nutzen und das ganz ohne Zusatzaufwand.

README.me

@@ -1,3 +1,4 @@
 Codewars
 Aufgabe 1 Snail: https://www.codewars.com/kata/521c2db8ddc89b9b7a0000c1
 Aufgabe 2 Vigenère Cipher Helper: https://www.codewars.com/kata/52d1bd3694d26f8d6e0000d3
+Aufgabe 3 PaginationHelper: https://www.codewars.com/kata/515bb423de843ea99400000a

src/codewars/pagination_helper.py

@@ -0,0 +1,42 @@
+import math
+
+
+class PaginationHelper:
+
+    # The constructor takes in an array of items and an integer indicating
+    # how many items fit within a single page
+    def __init__(self, collection, items_per_page):
+        self.collection = collection
+        self.items_per_page = items_per_page
+
+    # returns the number of items within the entire collection
+    def item_count(self):
+        return len(self.collection)
+
+    # returns the number of pages
+    def page_count(self):
+        item_count = self.item_count()
+        return math.ceil(item_count / self.items_per_page)
+
+    # returns the number of items on the given page. page_index is zero based
+    # this method should return -1 for page_index values that are out of range
+    def page_item_count(self, page_index):
+        number_of_pages = self.page_count()
+        if page_index > number_of_pages - 1 or page_index < 0:
+            return -1
+
+        item_count = self.item_count()
+        page_count_without_round_up = item_count / self.items_per_page
+
+        if page_count_without_round_up - page_index > 1:
+            return self.items_per_page
+        else:
+            return item_count - page_index * self.items_per_page
+
+    # determines what page an item at the given index is on. Zero based indexes.
+    # this method should return -1 for item_index values that are out of range
+    def page_index(self, item_index):
+        if item_index < 0 or item_index >= self.item_count():
+            return -1
+
+        return item_index // self.items_per_page