Merge pull request #34 from Pratyush2703/doubly-linked-list

Doubly linked list

Author: Bhrigu Kansra

Data Structures/DoubleLinkedList.py

@@ -0,0 +1,131 @@
+#Defined Node
+class ListNode:  
+    def __init__(self, data):
+        "constructor class to initiate this object"
+
+        # store data
+        self.data = data
+
+        # store reference (next item)
+        self.next = None
+
+        # store reference (previous item)
+        self.previous = None
+        return
+
+    def has_value(self, value):
+        "method to compare the value with the node data"
+        if self.data == value:
+            return True
+        else:
+            return False
+            
+ #Doubly Linked List
+ 
+ class DoubleLinkedList:  
+    def __init__(self):
+        "constructor to initiate this object"
+
+        self.head = None
+        self.tail = None
+        return
+
+    def list_length(self):
+        "returns the number of list items"
+
+        count = 0
+        current_node = self.head
+
+        while current_node is not None:
+            # increase counter by one
+            count = count + 1
+
+            # jump to the linked node
+            current_node = current_node.next
+
+        return count
+
+    def output_list(self):
+        "outputs the list (the value of the node, actually)"
+        current_node = self.head
+
+        while current_node is not None:
+            print(current_node.data)
+
+            
+            current_node = current_node.next
+
+        return
+
+    def unordered_search (self, value):
+        "search the linked list for the node that has this value"
+
+        
+        current_node = self.head
+
+        
+        node_id = 1
+
+        
+        results = []
+
+        while current_node is not None:
+            if current_node.has_value(value):
+                results.append(node_id)
+
+            
+            current_node = current_node.next
+            node_id = node_id + 1
+
+        return results
+        
+        #Adding nodes
+        
+def add_list_item(self, item):
+        "add an item at the end of the list"
+
+        if isinstance(item, ListNode):
+            if self.head is None:
+                self.head = item
+                item.previous = None
+                item.next = None
+                self.tail = item
+            else:
+                self.tail.next = item
+                item.previous = self.tail
+                self.tail = item
+
+        return
+        
+        #Removing Nodes
+       
+ def remove_list_item_by_id(self, item_id):
+        "remove the list item with the item id"
+
+        current_id = 1
+        current_node = self.head
+
+        while current_node is not None:
+            previous_node = current_node.previous
+            next_node = current_node.next
+
+            if current_id == item_id:
+                # if this is the first node (head)
+                if previous_node is not None:
+                    previous_node.next = next_node
+                    if next_node is not None:
+                        next_node.previous = previous_node
+                else:
+                    self.head = next_node
+                    if next_node is not None:
+                        next_node.previous = None
+                # we don't have to look any further
+                return
+
+            # needed for the next iteration
+            current_node = next_node
+            current_id = current_id + 1
+
+        return
+        
+