Python - Delete even nodes of the Circular Doubly Linked List
Deleting even nodes of a circular doubly linked list requires traverse through the list and deleting even nodes one by one. It requires creating two nodes - oddNode and evenNode. If the list contains more than one node, make oddNode to first odd node of list and evenNode to first even node of the list. Store the current odd node into temp node and delete the even node. Move both nodes to next set of odd-even nodes. Repeat the process till any of nodes reaches head. Finally, link the last node with the head.
The function deleteEvenNodes is created for this purpose. It is a 3-step process.
def deleteEvenNodes(self): if (self.head != None and self.head.next != self.head): #1. if the list has more than one element # create evenNode node - pointing to head # oddNode node - pointing to next of head # temp node - to store last odd node oddNode = self.head evenNode = self.head.next while(True): #2. delete even node and update evenNode and # oddNode to next set of odd-even nodes # update temp node to latest oddNode node # continue the process till any of the node # reaches head temp = oddNode oddNode.next = evenNode.next oddNode.next.prev = oddNode evenNode = None oddNode = oddNode.next evenNode = oddNode.next if(oddNode == self.head or evenNode == self.head): break #3. if oddNode reaches head, make next of # temp as head else make next of oddNode # as head if(oddNode == self.head): temp.next = self.head self.head.prev = temp else: oddNode.next = self.head self.head.prev = oddNode
The below is a complete program that uses above discussed concept of deleting even nodes of a circular 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 newNode.next = self.head newNode.prev = self.head return else: temp = self.head while(temp.next != self.head): temp = temp.next temp.next = newNode newNode.next = self.head newNode.prev = temp self.head.prev = newNode #delete even nodes of the list def deleteEvenNodes(self): if (self.head != None and self.head.next != self.head): oddNode = self.head evenNode = self.head.next while(True): temp = oddNode oddNode.next = evenNode.next oddNode.next.prev = oddNode evenNode = None oddNode = oddNode.next evenNode = oddNode.next if(oddNode == self.head or evenNode == self.head): break if(oddNode == self.head): temp.next = self.head self.head.prev = temp else: oddNode.next = self.head self.head.prev = oddNode #display the content of the list def PrintList(self): temp = self.head if(temp != None): print("The list contains:", end=" ") while (True): print(temp.data, end=" ") temp = temp.next if(temp == self.head): break print() else: print("The 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("After 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