London | 25-SDC-July | Andrei Filippov | Sprint 2 | Implement a linked list in Python

Sprint-2/implement_linked_list/linked_list.py

@@ -0,0 +1,58 @@
+class Node:
+    def __init__(self, value):
+        self.value = value
+        self.previous = None
+        self.next = None
+
+
+class LinkedList:
+    def __init__(self):
+        self.head = None
+        self.tail = None
+
+    def push_head(self, element):
+        node = Node(element)
+        if self.head:
+            node.next = self.head
+            self.head.previous = self.head = node
+        else:
+            self.head = node
+            self.tail = node
+        return node
+
+    def pop_tail(self):
+        # get current tail
+        node = self.tail
+        if self.tail is not self.head:
+            # replace the tail
+            self.tail = node.previous
+            # reset to none
+            self.tail.next = node.previous = None
+        else:
+            self.head = None
+            self.tail = None
+            node.previous = None
+            node.next = None
+        return node.value
+
+    def remove(self, node):
+        if self.head == node:
+            if self.tail == node:
+                # head == node, tail == node
+                self.head = self.tail = None
+                node.previous = None
+                node.next = None
+            else:
+                # head == node, tail != node
+                self.head = node.next
+                self.head.previous = node.next = None
+        else:
+            if self.tail == node:
+                # head != node, tail == node
+                self.tail = node.previous
+                self.tail.next = node.previous = None
+            else:
+                # head != node, tail != node
+                node.previous.next = node.next
+                node.next.previous = node.previous
+                node.previous = node.next = None

Sprint-2/implement_linked_list/linked_list_test.py

@@ -2,6 +2,7 @@
 
 from linked_list import LinkedList
 
+
 class LinkedListTest(unittest.TestCase):
     def test_pushes_then_pops(self):
         l = LinkedList()
@@ -34,6 +35,32 @@ def test_remove_tail(self):
         self.assertIsNone(b.next)
         self.assertIsNone(b.previous)
 
+    def test_remove_last(self):
+        l = LinkedList()
+        a = l.push_head("a")
+        b = l.push_head("b")
+        l.remove(a)
+        l.remove(b)
+        self.assertIsNone(a.next)
+        self.assertIsNone(a.previous)
+        self.assertIsNone(b.next)
+        self.assertIsNone(b.previous)
+        self.assertIsNone(l.head)
+        self.assertIsNone(l.tail)
+
+    def test_pop_last_tail(self):
+        l = LinkedList()
+        a = l.push_head("a")
+        b = l.push_head("b")
+        c = l.push_head("c")
+        l.remove(a)
+        l.remove(c)
+        l.pop_tail()
+        self.assertIsNone(b.next)
+        self.assertIsNone(b.previous)
+        self.assertIsNone(l.head)
+        self.assertIsNone(l.tail)
+
 
 if __name__ == "__main__":
     unittest.main()