Python - Delete even nodes of the Doubly Linked List
Deleting even nodes of a doubly linked list requires traverse through the list and deleting even nodes one by one. It requires creating two nodes - oddNode and evenNode. If head is not null, make oddNode to first odd node of list and evenNode to first even node of the list. If both are not null, delete the evenNode and adjust links. Move both nodes to next set of odd-even nodes. Repeat the process till any or both nodes become null.
The function deleteEvenNodes is created for this purpose. It is a 4-step process.
def deleteEvenNodes(self): if (self.head != None): #1. if head is not null create nodes - # evenNode and oddNode oddNode = self.head evenNode = self.head.next while(oddNode != None and evenNode != None): #2. while oddNode and evenNode are not null # make next of oddNode as next of evenNode # and free evenNode oddNode.next = evenNode.next evenNode = None #3. and make temp as oddNode and oddNode as # next of oddNode temp = oddNode oddNode = oddNode.next #4. Update prev link, oddNode and evenNode if(oddNode != None): oddNode.prev = temp evenNode = oddNode.next
The below is a complete program that uses above discussed concept of deleting even nodes of a doubly linked list.
# node structure class Node: def __init__(self, data): self.data = data self.next = None self.prev = None #class Linked List class LinkedList: def __init__(self): self.head = None #Add new element at the end of the list def push_back(self, newElement): newNode = Node(newElement) if(self.head == None): self.head = newNode return else: temp = self.head while(temp.next != None): temp = temp.next temp.next = newNode newNode.prev = temp #delete even nodes of the list def deleteEvenNodes(self): if (self.head != None): oddNode = self.head evenNode = self.head.next while(oddNode != None and evenNode != None): oddNode.next = evenNode.next evenNode = None temp = oddNode oddNode = oddNode.next if(oddNode != None): oddNode.prev = temp evenNode = oddNode.next #display the content of the list def PrintList(self): temp = self.head if(temp != None): print("\nThe list contains:", end=" ") while (temp != None): print(temp.data, end=" ") temp = temp.next else: print("\nThe list is empty.") # test the code MyList = LinkedList() #Add five elements in the list. MyList.push_back(10) MyList.push_back(20) MyList.push_back(30) MyList.push_back(40) MyList.push_back(50) #Display the content of the list. MyList.PrintList() #delete even nodes of the list MyList.deleteEvenNodes() print("\nAfter deleting even nodes.") #Display the content of the list. MyList.PrintList()
The above code will give the following output:
The list contains: 10 20 30 40 50 After deleting even nodes. The list contains: 10 30 50