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1. 1. Linked List Interview Prep Spencer Moran 11/20/13
2. 2. Why Linked Lists? • Simplicity • Little variation • Pointers and references
3. 3. Singly Linked List Almost all LL interview questions are based on singly linked lists
4. 4. Doubly Linked List
5. 5. Implementation • Can be implemented as an ADT • Often use templates • List is referred to by the head, the first node in the list • If you modify the list, you must return the head of the new list
6. 6. Traversal
7. 7. Insertion
8. 8. Deletion
9. 9. Linked List Question Strategies • Use two (or more??) pointers to traverse the list • Traverse pointers at different speeds • Use an additional data structure
10. 10. Common Linked List Questions Find the kth to last element in a singly linked list.
11. 11. Strategy • Use multiple pointers to traverse the list. • Return an error if the list is not at least k nodes long. • Traverse the list with 2 pointers: – Pointer1 starts at head – Pointer2 starts k nodes in front of the head. – When pointer2 reaches the end of the list, return pointer1
12. 12. Common Linked List Questions Determine if a singly linked list has a loop or cycle.
13. 13. Strategy • Use multiple pointers and traverse them at different speeds. • Start both pointers at head: – Traverse the list, moving fast pointer twice as fast as the slow pointer. – If fast pointer reaches the end of the list, there is no cycle. – If the pointers ever are equal to one another, there is a cycle.
14. 14. BONUS QUESTION Determine if a linked list has a cycle. If it does, return the element where the cycle begins.
15. 15. Bonus Question #2 Find the length of the cycle without traversing it multiple times.
16. 16. Common Linked List Questions Reverse a singly linked list.
17. 17. Strategy • Use an additional data structure. • Traverse the list, pushing each node into the stack. • Set the new head equal to the first element in the list. • Starting at the new head, add the top element from the stack until the stack is empty.
18. 18. Other common questions • Remove duplicates from a singly linked list • Merge sort • Remove element from middle of list (without head) • Check if the linked list is a palindrome • Fold a singly linked list using no containers
19. 19. Meeting Summary We also covered a bunch of questions at the end of the meeting. These questions were mostly about linked lists, but we also started covering trees and decided that trees and graphs will be our next topic. The date of our next meeting will be arranged through the facebook group.