solution.py

# PaginationHelper
# For this exercise you will be strengthening your page-fu mastery.
# You will complete the PaginationHelper class,
# which is a utility class helpful for querying paging information related to an array.

# The class is designed to take in an array of values
# and an integer indicating how many items will be allowed per each page.
# The types of values contained within the collection/array are not relevant.

# The following are some examples of how this class is used:

# helper = PaginationHelper(['a','b','c','d','e','f'], 4)
# helper.page_count # should == 2
# helper.item_count # should == 6
# helper.page_item_count(0)  # should == 4
# helper.page_item_count(1) # last page - should == 2
# helper.page_item_count(2) # should == -1 since the page is invalid

# page_ndex takes an item index and returns the page that it belongs on
# helper.page_index(5) # should == 1 (zero based index)
# helper.page_index(2) # should == 0
# helper.page_index(20) # should == -1
# helper.page_index(-10) # should == -1 because negative indexes are invalid


import math


class PaginationHelper:
    # The constructor takes in an array of items and a 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):
        return int(math.ceil(1.0 * self.item_count() / self._items_per_page))

    # returns the number of items on the current 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):
        if (page_index + 1) * self._items_per_page <= self.item_count():
            return self._items_per_page

        if page_index * self._items_per_page < self.item_count() < (page_index + 1) * self._items_per_page:
            return self.item_count() % self._items_per_page

        return -1

    # determines what page an item 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 self.item_count() > item_index >= 0:
            return int(item_index / self._items_per_page)

        return -1