Insert at Beginning Head Insert in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Insert at Beginning' mean in a linked list?

It means adding a new node at the start (head) of the linked list, making it the first element.

beginner

Why is inserting at the beginning of a linked list efficient?

Because it only requires changing the head pointer and the new node's next pointer, which takes constant time O(1).

intermediate

In C, what pointer changes are needed to insert a new node at the beginning of a singly linked list?

Set the new node's next pointer to the current head, then update the head pointer to the new node.

beginner

What happens to the old head node after inserting a new node at the beginning?

The old head becomes the second node in the list, as the new node points to it.

intermediate

Show the basic C code snippet to insert a node at the beginning of a singly linked list.

struct Node* newNode = malloc(sizeof(struct Node)); newNode->data = value; newNode->next = head; head = newNode;

What is the time complexity of inserting a node at the beginning of a singly linked list?

A O(n)

B O(1)

C O(log n)

D O(n^2)

Inserting at the beginning only changes a few pointers, so it takes constant time O(1).

Which pointer must be updated to insert a new node at the beginning of a linked list?

A The head pointer

B The tail pointer

C The next pointer of the last node

D The previous pointer

The head pointer must point to the new node after insertion.

After inserting a new node at the beginning, what does the new node's next pointer point to?

A NULL

B The tail node

C The old head node

D Itself

The new node's next pointer points to the old head node, linking the list.

Which of these is NOT needed when inserting at the beginning of a singly linked list in C?

A Allocating memory for the new node

B Changing the new node's next pointer

C Updating the head pointer

D Traversing the entire list

Traversing the list is not needed because insertion is at the head.

What happens if you forget to update the head pointer after inserting a new node at the beginning?

A The list will lose the new node and may cause errors

B The new node becomes the tail

C The list remains unchanged

D The list will reverse

Without updating head, the new node is not linked as the first node, causing loss of access.

Explain step-by-step how to insert a new node at the beginning of a singly linked list in C.

Think about how pointers change to keep the list connected.

Describe why inserting at the beginning of a linked list is faster than inserting at the end.

Consider how many nodes you must visit for each insertion.