Insert a node at the head of a linked list using C++ You’re given the pointer to
ID: 3904361 • Letter: I
Question
Insert a node at the head of a linked list using C++
You’re given the pointer to the head node of a linked list and an integer to add to the list. Create a new node with the given integer, insert this node at the head of the linked list and return the new head node. The head pointer given may be null meaning that the initial list is empty.
Input Format
You have to complete the SinglyLinkedListNode Insert(SinglyLinkedListNode head, int data) method which takes two arguments - the head of the linked list and the integer to insert. You should NOT read any input from stdin/console.
The input is handled by code in the editor and is as follows:
The first line contains an integer n , denoting the number of elements to be inserted at the head of the list. The next n lines contain an integer each, denoting the element to be inserted.
Constraints
Output Format
Insert the new node at the head and return the head of the updated linked list. Do NOT print anything to stdout/console.
The output is handled by the code in the editor and it is as follows:
Print the elements of linked list from head to tail, each in a new line.
Sample Input
5
383
484
392
975
321
Sample Output
321
975
392
484
383
Explanation
Intially the list in NULL. After inserting 383, the list is 383 -> NULL.
After inserting 484, the list is 484 -> 383 -> NULL.
After inserting 392, the list is 392 -> 484 -> 383 -> NULL.
After inserting 975, the list is 975 -> 392 -> 484 -> 383 -> NULL.
After inserting 321, the list is 321 -> 975 -> 392 -> 484 -> 383 -> NULL.
/*
* For your reference:
*
* SinglyLinkedListNode {
* int data;
* SinglyLinkedListNode* next;
* };
*
*/
SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* llist, int data) {
}
Please explain the insertNodeAtHead and add comments to as many code lines as possible. Explain how you added a node at the head of a linked list. How is this different from inserting a node at the tail?
Explanation / Answer
SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* llist, int data) {
SinglyLinkedListNode* n = new SinglyLinkedListNode(); //allocate a new node node
n->data = data; //set the data into the new node
n->next = llist; //make the new node point to the first node/head of existing list
return n ; //return the new node as the new head
}
Insertion at head is simple and does not need to check the case when list is empty. It simply needs to link the new node to existing list.
The new node is always the updated head node.