Linked List Problems

Successful candidates master a few core patterns that solve nearly all linked list interview questions.

1. Reverse a Linked List

The classic problem: reverse the pointers of a list in-place.

def reverse_list(head):
    prev = None
    curr = head
    while curr:
        next_node = curr.next
        curr.next = prev
        prev = curr
        curr = next_node
    return prev

2. Detect a Cycle (Floyd's Algorithm)

Use "Fast and Slow" pointers (Tortoise and Hare). If there is a cycle, they will eventually meet.

Key Patterns

• Two Pointers: Used for finding the middle or Nth from end.
• Fast & Slow Pointers: Used for cycle detection.
• Dummy Head: Used to simplify edge cases when modifying the list head.