Fixes for append and delete methods in linked list classes

Chapter04/CircularList.py

@@ -3,10 +3,8 @@ class Node:
     def __init__(self, data=None):
         self.data = data
         self.next = None
-
-
-
-
+
+
 class CircularList:
     def __init__ (self):
         self.tail = None
@@ -16,13 +14,13 @@ def __init__ (self):
     def append(self, data):  
         node = Node(data) 
         if self.tail: 
-            self.tail.next = node  
-            self.tail = node
+            self.tail.next = node
             node.next = self.head
+            self.tail = node
         else: 
             self.head = node 
             self.tail = node 
-            self.tail.next = self.tail
+            self.tail.next = self.head
         self.size += 1 
 
     def delete(self, data):

Chapter04/append_at_any_location_singly_linkedlist.py

@@ -4,7 +4,7 @@ def __init__(self, data=None):
         self.data = data
         self.next = None
 
-        
+
 class SinglyLinkedList:
     def __init__ (self):
         self.tail = None
@@ -15,38 +15,39 @@ def append(self, data):
         # Encapsulate the data in a Node 
         node = Node(data)
         if self.head is None:
-            self.head = node    
+            self.head = node
         else: 
             current = self.head 
             while current.next:
                 current = current.next 
             current.next = node
+        self.size += 1
 
     def append_at_a_location(self, data, index):  
         current = self.head  
         prev = self.head  
         node = Node(data) 
         count = 1 
-        while current: 
-            if count == 1:         
+        if index == 1:         
                 node.next = current 
                 self.head = node 
+                self.size += 1
                 print(count) 
-                return 
-            elif index == index: 
-                node.next = current  
-                prev.next = node 
-                return 
-            count += 1 
-            prev = current 
-            current = current.next 
+                return
+        else:
+            while current:  
+                if count == index: 
+                    node.next = current  
+                    prev.next = node
+                    self.size += 1
+                    return 
+                count += 1 
+                prev = current 
+                current = current.next 
         if count < index: 
             print("The list has less number of elements") 
 
-
-
-
-
+
 words = SinglyLinkedList()
 words.append('egg')
 words.append('ham')
@@ -56,9 +57,7 @@ def append_at_a_location(self, data, index):
 while current:
     print(current.data)
     current = current.next
-
-
-
+
 words.append_at_a_location('new', 2)
 
 current = words.head

Chapter04/delete_operation_doubly_linkedlist.py

@@ -3,12 +3,13 @@ def __init__ (self, data = None, next = None, prev = None):
         self.data = data 
         self.next = next
         self.prev = prev
-
+
+
 class DoublyLinkedList:
     def __init__ (self):
         self.head = None
         self.tail = None
-        self.count = 0
+        self.size = 0
 
     def append(self, data):
         #Append an item to the list.   
@@ -20,9 +21,7 @@ def append(self, data):
             new_node.prev = self.tail 
             self.tail.next = new_node 
             self.tail = new_node
-            self.count += 1 
-
-
+        self.size += 1 
 
     def delete(self, data):
         # Delete a node from the list. 
@@ -31,15 +30,15 @@ def delete(self, data):
         if current is None:       #List is empty
             print("List is empty")
         elif current.data == data:   #Item to be deleted is found at starting of list
-            self.head.prev = None 
-            node_deleted = True 
             self.head = current.next
+            self.head.prev = None
+            node_deleted = True
 
         elif self.tail.data == data:   #Item to be deleted is found at the end of list.
-            self.tail = self.tail.prev  
-            self.tail.next = None 
-            node_deleted = True 
-
+            self.tail = self.tail.prev
+            self.tail.next = None
+            node_deleted = True
+            
         else: 
             while current:          #search item to be deleted, and delete that node
                 if current.data == data: 
@@ -50,11 +49,9 @@ def delete(self, data):
             if node_deleted == False:   #Item to be deleted is not found in the list
                 print("Item not found")
         if node_deleted: 
-            self.count -= 1
+            self.size -= 1
+
 
-
-
-
 #Code to create for a doubly linked list
 words = DoublyLinkedList()
 words.append('egg')

Chapter04/delete_operation_singly_linkedlist.py

@@ -4,6 +4,7 @@ def __init__(self, data=None):
         self.data = data
         self.next = None
 
+
 class SinglyLinkedList:
     def __init__ (self):
         self.head = None
@@ -13,21 +14,22 @@ def append(self, data):
         # Encapsulate the data in a Node 
         node = Node(data)
         if self.head is None:
-            self.head = node    
+            self.head = node
         else: 
             current = self.head 
             while current.next:
-                current = current.next 
+                current = current.next
             current.next = node
+        self.size += 1
 
     def delete_first_node (self): 
         current = self.head  
         if self.head is None:
             print("No data element to delete")
         elif current == self.head:
             self.head = current.next
-
-          
+            self.size -= 1
+
     def delete_last_node (self): 
         current = self.head 
         prev = self.head
@@ -37,8 +39,7 @@ def delete_last_node (self):
                 self.size -= 1
             prev = current
             current = current.next
-
-
+
     def delete(self, data): 
         current = self.head 
         prev = self.head 

Chapter04/doubly_linked_list.py

@@ -3,12 +3,13 @@ def __init__ (self, data = None, next = None, prev = None):
         self.data = data 
         self.next = next
         self.prev = prev
-
+
+
 class DoublyLinkedList:
     def __init__ (self):
         self.head = None
         self.tail = None
-        self.count = 0
+        self.size = 0
 
     def append(self, data):
         #Append an item at the end of the list.   
@@ -20,7 +21,7 @@ def append(self, data):
             new_node.prev = self.tail 
             self.tail.next = new_node 
             self.tail = new_node
-        self.count += 1
+        self.size += 1
 
 
     def append_at_start(self, data):
@@ -33,7 +34,7 @@ def append_at_start(self, data):
             new_node.next = self.head 
             self.head.prev = new_node 
             self.head = new_node
-        self.count += 1
+        self.size += 1
 
     def append_at_a_location(self, data): 
         current = self.head 
@@ -45,7 +46,7 @@ def append_at_a_location(self, data):
                 new_node.next = current
                 prev.next = new_node
                 current.prev = new_node
-                self.count += 1
+                self.size += 1
             prev = current
             current = current.next            
 
@@ -66,8 +67,6 @@ def contains(self, data):
         return   
 
 
-
-
 words = DoublyLinkedList()
 words.append('egg')
 words.append('ham')

Chapter04/faster_append_singly_linked_list.py

@@ -19,6 +19,7 @@ def append(self, data):
         else:
             self.head = node 
             self.tail = node
+        self.size += 1
 
 
 words = SinglyLinkedList()

Chapter04/list_traversal_singly_linklist.py

@@ -14,21 +14,22 @@ def append(self, data):
         # Encapsulate the data in a Node 
         node = Node(data)
         if self.head is None:
-            self.head = node    
+            self.head = node
         else: 
             current = self.head 
             while current.next:
-                current = current.next 
+                current = current.next
             current.next = node
-
+        self.size += 1   
+
     def iter(self):
         current = self.head 
         while current:
             val = current.data 
             current = current.next 
             yield val
 
-            
+
 words = SinglyLinkedList()
 words.append('egg')
 words.append('ham')