Add First - codepath/compsci_guides GitHub Wiki

Unit 5 Session 2 (Click for link to problem statements)

U-nderstand

Understand what the interviewer is asking for by using test cases and questions about the problem.

• What does the function return if new_node is added to an empty linked list?
  • The function should return the new_node as it becomes the head of the linked list, even if the list was previously empty.

P-lan

Plan the solution with appropriate visualizations and pseudocode.

General Idea: Modify the linked list by inserting a new node at the beginning and updating the head of the list to this new node.

1) Set the `next` attribute of the `new_node` to the current `head` of the linked list.
2) Return `new_node`, as it is now the new head of the list.

⚠️ Common Mistakes

• Returning the old head instead of the new_node.
• Not handling the next attribute correctly, which could lead to losing the rest of the list.

I-mplement

def add_first(head, new_node):
  new_node.next = head
  return new_node