linked list

Author: Emilianouz

Sprint-2/implement_linked_list/linked_list.py

@@ -3,57 +3,57 @@
 # `pop_tail` should remove an element from the end of the list.
 # `remove` takes a handle from `push_head`, and removes that element from the list.
 
-class LinkedList:
-    class _Node:  # to have O(1) must be implemented double linked list to access previous
-        __slots__ = ("value", "prev", "next")
+class Node:
+    def __init__(self, value):
+        self.value = value      
+        self.prev = None        
+        self.next = None       
 
-        def __init__(self, value):
-            self.value = value
-            self.prev = None
-            self.next = None
 
+class LinkedList:
     def __init__(self):
-        self.head = None
-        self.tail = None
+        self.head = None        
+        self.tail = None        
 
+    # adding a new value in the front of the list
     def push_head(self, value):
-        node = self._Node(value)
+        node = Node(value)      
 
-        node.next = self.head
-        if self.head:
-            self.head.prev = node
+        if self.head is None:   # if list is empty head and tail becomes this node.
+            self.head = node    
+            self.tail = node    
         else:
-            # when list gets empty, tail also becomes this node
-            self.tail = node
+            node.next = self.head   
+            self.head.prev = node   
+            self.head = node        
 
-        self.head = node
-        return node  # handling
+        return node  # returns the node so we can remove it later
 
+    # removing last element
     def pop_tail(self):
-        if not self.tail:
-            raise IndexError("pop from empty list")
+        if self.tail is None:   
+            raise Exception("List is empty")
 
-        node = self.tail
-        value = node.value
+        value = self.tail.value  # value to return
 
-        self.tail = node.prev
-        if self.tail:
-            self.tail.next = None
-        else:
-            # when the list gets empty
+        if self.head == self.tail:  # if only one element
             self.head = None
+            self.tail = None
+        else:
+            self.tail = self.tail.prev  # move tail back
+            self.tail.next = None       # remove old tail connection
 
         return value
 
+    # removes a specific node 
     def remove(self, node):
-        if node.prev:
-            node.prev.next = node.next
-        else:
-            # removes head
-            self.head = node.next
 
-        if node.next:
-            node.next.prev = node.prev
+        if node.prev is None:   # if removing head
+            self.head = node.next
         else:
-            # removes tail
+            node.prev.next = node.next  # connect previous to next
+
+        if node.next is None:   # if removing tail
             self.tail = node.prev
+        else:
+            node.next.prev = node.prev  # connect next to previous