# UGC-NET | UGC NET CS 2016 Aug – II | Question 21

Consider an implementation of unsorted single linked list. Suppose it has its representation with a head and a tail pointer (i.e. pointers to the first and last nodes of the linked list). Given the representation, which of the following operation can not be implemented in O(1) time ?**(A)** Insertion at the front of the linked list.**(B)** Insertion at the end of the linked list.**(C)** Deletion of the front node of the linked list.**(D)** Deletion of the last node of the linked list.**Answer:** **(D)****Explanation:**

Deletion of the last node of the linked list, we need address of second last node of single linked list to make NULL of its next pointer. Since we can not access its previous node in singly linked list, so need to traverse entire linked list to get second last node of linked list.

So, option (D) is correct.

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