Insertion at the head of Linked List - DSA Practice

Given the head of a singly linked list and an integer X, insert a node with value X at the head of the linked list and return the head of the modified list.

Example 1:

Input: linkedList = [1, 2, 3], X = 7

Output: [7, 1, 2, 3]

Explanation:

7 was added as the 1st node.

Example 2:

Input: linkedList = [], X = 7

Output: [7]

Explanation:

7 was added as the 1st node.

Now Your Turn!

Pick the correct output for the given input

Input: [1, 3], X = 4

[1, 3, 4][4,1, 3][1][4, 3, 1]

Still unsure what the problem is asking ?

Let’s go through a few more examples, step by step, to make it clearer.

Constraints:

0 <= number of nodes in the Linked List <= 1000
0 <= ListNode.val <= 100
0 <= X <= 100

Hints

Frequently Occurring Doubts

Interview Follow-up Questions

Tab-1

1/*
2Definition of singly linked list:
3class ListNode{
4  public:
5    int data;
6    ListNode *next;
7    ListNode() : data(0), next(nullptr) {}
8    ListNode(int x) : data(x), next(nullptr) {}
9    ListNode(int x, ListNode *next) : data(x), next(next) {}
10};
11*/
12 
13class Solution {
14    public:
15        ListNode* insertAtHead(ListNode* &head, int X) {
16            //your code goes here
17        }
18};

Input:

Linked List

Example 1:

Example 2:

Now Your Turn!

Constraints:

Hints

Hint 1

Hint 2

Frequently Occurring Doubts

What is the difference between inserting at the head and at other positions?

How do you ensure the rest of the list remains intact?

Interview Follow-up Questions

How would you handle a circular linked list?

What if you frequently need to insert at the head?