Understand the Problem

We are given a function called insertNodeAtPosition, which has three parameters, head, data, and position.

Our head is a SinglyLinkedListNode (class) pointer to the head of the list, our data is an integer value to insert as data in a new node which we will create, and the position is a zero based index position to where we should insert our new node.

head: pointer to the head of the list
data: integer value of our new node (1)
position: a zero based index position (2)

In order to insert a Node at a specific position in the singly linked list, we must create a new node with our data parameter, insert it at the position we were given, and return the head node.

Example:

If our list starts as
4 -> 6 -> 2 -> 9
and our position = 2 and our data = 3\. Our new list will be
4 -> 6 -> 3 -> 2 -> 9

We must return a reference to the head node of our finished list.

---

Plan

We know that our first step will have to be to create a new node in order to have one to insert. Taking a look at our SinglyLinkedListNode class, we can see that it is expecting data to be passed in.

class SinglyLinkedListNode:
    def __init__(self, node_data):
        self.data = node_data
        self.next = None

We can create a new node in our insertNodeAtPosition function definition by setting new to SinglyLinkedListNode(data).

new = SinglyLinkedListNode(data)

We know that our position is index value 2, so we’ll need to set a pointer to the head in order to traverse through the list from the very beginning, and also set a counter in order to move our pointer through the list node by node, until we reach our given position.

pointer = head    
counter = 1

We will need to traverse through the list in order reach our position, starting with the head. Since our pointer is already set to the head, we can use a while loop that will traverse through the list until pointer.next is at our given position. We do this while pointer.next is not None.

while pointer.next is not None:

We will traverse through the list position by position, with our pointer, until we are at our given position, setting counter to counter + 1.

counter += 1
pointer = pointer.next

If pointer.next is finally at our given position, where our counter would be equal to our position of 2, we would set new.next to point to pointer.next.

#software-engineering #hackerrank #algorithms #coding #women-in-tech