# Python - Delete a node at the given position in the Circular Singly Linked List

In this method, a node at the specified position in the circular singly linked list is deleted. For example - if the given list is 10->20->30 and the 2^{nd} node is deleted, the list becomes 10->20.

First, create two nodes *temp* and *nodeToDelete* to traverse through the list and track the node to delete respectively. After that count the number of elements in the list to check whether the specified position is valid or not (It must lie in the range of [1, *n*], where *n* is number of elements in the list). If the specified valid position is 1 and head is the only element in the list, then make the head as null. If the specified valid position is 1 and list contains more than one elements, then make next of head as new head and adjust links accordingly. If the specified valid position is greater than 1 then traverse to the node previous to the given position and delete the given node and adjust links accordingly.

The function *pop_at* is created for this purpose. It is a **5-step process**.

def pop_at(self, position): #1. create two nodes - temp and nodeToDelete # to traverse and track the node to delete nodeToDelete = self.head temp = self.head NoOfElements = 0 #2. Find the number of elements in the list if(temp != None): NoOfElements += 1 temp = temp.next while(temp != self.head): NoOfElements += 1 temp = temp.next #3. check if the specified position is valid if(position < 1 or position > NoOfElements): print("\nInavalid position.") elif (position == 1): #4. if the position is 1 and head is the only element # in the list, then make it null, else make next # of head as new head and adjust links accordingly if(self.head.next == self.head): self.head = None else: while(temp.next != self.head): temp = temp.next self.head = self.head.next temp.next = self.head nodeToDelete = None else: #5. Else, traverse to the node previous to # the given position and delete the given # node and adjust links accordingly temp = self.head for i in range(1, position-1): temp = temp.next nodeToDelete = temp.next temp.next = temp.next.next nodeToDelete = None

The below is a complete program that uses above discussed concept to delete a node at a given position in the circular singly linked list.

# node structure class Node: def __init__(self, data): self.data = data self.next = 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 return else: temp = self.head while(temp.next != self.head): temp = temp.next temp.next = newNode newNode.next = self.head #Delete an element at the given position def pop_at(self, position): nodeToDelete = self.head temp = self.head NoOfElements = 0 if(temp != None): NoOfElements += 1 temp = temp.next while(temp != self.head): NoOfElements += 1 temp = temp.next if(position < 1 or position > NoOfElements): print("\nInavalid position.") elif (position == 1): if(self.head.next == self.head): self.head = None else: while(temp.next != self.head): temp = temp.next self.head = self.head.next temp.next = self.head nodeToDelete = None else: temp = self.head for i in range(1, position-1): temp = temp.next nodeToDelete = temp.next temp.next = temp.next.next nodeToDelete = None #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 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