[Issue - 608] - Add tests for Python Doubly Linked List

Author: Philip-W

Python/DataStructures/DoublyLinkedList/doubly_linked_list.py

@@ -0,0 +1,82 @@
+class Node:
+ def __init__(self, data=None, prev=None, next=None):
+ self.data = data
+ self.prev = prev
+ self.next = next
+
+
+class DoublyLinkedList:
+ def __init__(self):
+ self.head = None
+
+ def insert_at_beginning(self, data):
+ if self.head is None:
+ node = Node(data)
+ self.head = node
+ else:
+ new_head = Node(data, next=self.head)
+ self.head.prev = new_head
+ self.head = new_head
+
+ def length(self):
+ itr = self.head
+ count = 0
+ while itr:
+ count += 1
+ itr = itr.next
+ return count
+
+ def insert_at_end(self, data):
+ if self.head is None:
+ self.insert_at_beginning(data)
+ else:
+ itr = self.head
+ while itr.next:
+ itr = itr.next
+ itr.next = Node(data, prev=itr)
+
+ def insert_at(self, data, at):
+ if at == 0:
+ self.insert_at_beginning(data)
+ elif at == self.length() - 1 and self.length() > 2:
+ self.insert_at_end(data)
+ else:
+ itr = self.head
+ count = 0
+ while itr:
+ if count != at - 1:
+ count += 1
+ itr = itr.next
+ else:
+ break
+ itr.next = Node(data, itr, itr.next)
+
+ def remove_val(self, val):
+ while self.head and self.head.data is val:
+ self.head = self.head.next
+ if self.head is None:
+ return
+
+ current = self.head
+ while current:
+ if current.data == val:
+ if current == self.head:
+ self.head = current.next
+ self.head.prev = None
+ if current.next is None:
+ current.prev.next = None
+ return
+ else:
+ current.next.prev = current.prev
+ current.prev.next = current.next
+ current = current.next
+
+ def __str__(self):
+ current = self.head
+ as_string = ''
+ while current:
+ as_string += str(current.data)
+ if current.next:
+ as_string += ' --> '
+ current = current.next
+ return as_string

Python/DataStructures/DoublyLinkedList/test/test_doubly_linked_list.py

@@ -0,0 +1,106 @@
+import unittest
+from Python.DataStructures.DoublyLinkedList.doubly_linked_list import DoublyLinkedList
+
+class TestDoublyLinkedList(unittest.TestCase):
+
+ def test_list_is_empty_on_initialization(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ self.assertEqual(a_doubly_linked_list.length(), 0)
+
+ def test_adding_to_front_should_append_node_to_front(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ self.assertEqual(a_doubly_linked_list.length(), 1)
+ a_doubly_linked_list.insert_at_beginning(4)
+ self.assertEqual(a_doubly_linked_list.__str__(), "4 --> 5")
+
+ def test_adding_to_end_should_append_node_to_end(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ self.assertEqual(a_doubly_linked_list.length(), 1)
+ a_doubly_linked_list.insert_at_end(4)
+ self.assertEqual(a_doubly_linked_list.__str__(), "5 --> 4")
+ self.assertEqual(a_doubly_linked_list.length(), 2)
+
+ def test_insert_at_should_append_node_to_correct_position_for_a_short_list(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ a_doubly_linked_list.insert_at_beginning(3)
+
+ a_doubly_linked_list.insert_at(4, 1)
+ self.assertEqual(a_doubly_linked_list.__str__(), "3 --> 4 --> 5")
+ self.assertEqual(a_doubly_linked_list.length(), 3)
+
+ def test_insert_at_should_append_node_to_correct_position(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(2)
+ a_doubly_linked_list.insert_at_beginning(1)
+
+ a_doubly_linked_list.insert_at(3, 2)
+ self.assertEqual(a_doubly_linked_list.__str__(), "1 --> 2 --> 3 --> 4 --> 5")
+ self.assertEqual(a_doubly_linked_list.length(), 5)
+
+ def test_insert_at_should_insert_at_start(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ a_doubly_linked_list.insert_at_beginning(4)
+
+ a_doubly_linked_list.insert_at(3, 0)
+ self.assertEqual(a_doubly_linked_list.__str__(), "3 --> 4 --> 5")
+ self.assertEqual(a_doubly_linked_list.length(), 3)
+
+ def test_insert_at_should_insert_at_end_for_short_list(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ a_doubly_linked_list.insert_at_beginning(4)
+
+ a_doubly_linked_list.insert_at(6, 2)
+ self.assertEqual(a_doubly_linked_list.__str__(), "4 --> 5 --> 6")
+ self.assertEqual(a_doubly_linked_list.length(), 3)
+
+ def test_insert_at_should_insert_at_end(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(5)
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(4)
+
+ a_doubly_linked_list.insert_at(6, 4)
+ self.assertEqual(a_doubly_linked_list.__str__(), "4 --> 4 --> 4 --> 5 --> 6")
+ self.assertEqual(a_doubly_linked_list.length(), 5)
+
+ def test_remove_val_should_remove_values_from_list(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(3)
+ a_doubly_linked_list.insert_at_beginning(2)
+ a_doubly_linked_list.insert_at_beginning(1)
+
+ a_doubly_linked_list.remove_val(1)
+ self.assertEqual(a_doubly_linked_list.length(), 3)
+ self.assertEqual(a_doubly_linked_list.__str__(), "2 --> 3 --> 4")
+
+ def test_remove_val_should_remove_values_from_list_when_values_are_all_the_same(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(4)
+
+ a_doubly_linked_list.remove_val(4)
+ self.assertEqual(a_doubly_linked_list.length(), 0)
+ self.assertEqual(a_doubly_linked_list.__str__(), "")
+
+ def test_remove_val_should_remove_values_from_list_when_values_are_all_the_same_except_one(self):
+ a_doubly_linked_list = DoublyLinkedList()
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(5)
+ a_doubly_linked_list.insert_at_beginning(4)
+ a_doubly_linked_list.insert_at_beginning(4)
+
+ a_doubly_linked_list.remove_val(4)
+ self.assertEqual(a_doubly_linked_list.__str__(), "5")
+ self.assertEqual(a_doubly_linked_list.length(), 1)
+ self.assertEqual(a_doubly_linked_list.__str__(), "5")