Python - Delete a node at the given position in the Doubly Linked List
In this method, a node at the specified position in the doubly linked list is deleted. For example - if the given list is 10->20->30 and the 2nd node is deleted, the list becomes 10->20.
First, the specified position must be greater than equal to 1. If the specified position is 1 and head is not null, then make the head next as head and delete the previous head. Else, traverse to the node that is previous to the specified position. If the specified node and previous to the specified node are not null then adjust the link. In other case, the specified node will be already null. The below figure describes the process, if the deletion node is other than the head node.
The function pop_at is created for this purpose. It is a 5-step process.
def pop_at(self, position): #1. check if the position is > 0 if(position < 1): print("\nposition should be >= 1.") elif (position == 1 and self.head != None): #2. if the position is 1 and head is not null, make # head next as head and delete previous head nodeToDelete = self.head self.head = self.head.next nodeToDelete = None if (self.head != None): self.head.prev = None else: #3. Else, make a temp node and traverse to the # node previous to the position temp = self.head for i in range(1, position-1): if(temp != None): temp = temp.next #4. If the previous node and next of the previous # is not null, adjust links if(temp != None and temp.next != None): nodeToDelete = temp.next temp.next = temp.next.next if(temp.next.next != None): temp.next.next.prev = temp.next nodeToDelete = None else: #5. Else the given node will be empty. print("\nThe node is already null.")
The below is a complete program that uses above discussed concept to delete a node at a given position in the doubly linked list.
# node structure class Node: def __init__(self, data): self.data = data self.next = None self.prev = None #class LinkedList 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 an element at the given position def pop_at(self, position): if(position < 1): print("\nposition should be >= 1.") elif (position == 1 and self.head != None): nodeToDelete = self.head self.head = self.head.next nodeToDelete = None if (self.head != None): self.head.prev = None else: temp = self.head for i in range(1, position-1): if(temp != None): temp = temp.next if(temp != None and temp.next != None): nodeToDelete = temp.next temp.next = temp.next.next if(temp.next.next != None): temp.next.next.prev = temp.next nodeToDelete = None else: print("\nThe node is already null.") #display the content of the list def PrintList(self): temp = self.head if(temp != None): print("The list contains:", end=" ") while (temp != None): print(temp.data, end=" ") temp = temp.next print() else: print("The list is empty.") # test the code MyList = LinkedList() #Add three elements at the end of the list. MyList.push_back(10) MyList.push_back(20) MyList.push_back(30) MyList.PrintList() #Delete an element at position 2 MyList.pop_at(2) MyList.PrintList() #Delete an element at position 1 MyList.pop_at(1) MyList.PrintList()
The above code will give the following output:
The list contains: 10 20 30 The list contains: 10 30 The list contains: 30