Reverse a linked list iteratively and recursively.
Interviewer Expectations for this Question
01
Core Competency
Assesses fundamental understanding of Data Structures & Algorithms conventions, runtime behavior, and memory/performance considerations.
02
Evaluation Criteria
Hiring managers look for precision, avoidance of ambiguous jargon, and ability to explain trade-offs under real production conditions.
Comprehensive Model Answer
Verified Solution
Iterative (O(n) time, O(1) space):
def reverse(head):
prev = None
while head:
nxt = head.next
head.next = prev
prev = head
head = nxt
return prev
Recursive (O(n) time, O(n) stack space):
def reverse(head):
if not head or not head.next:
return head
new_head = reverse(head.next)
head.next.next = head
head.next = None
return new_head
Follow-ups: reverse a sublist between positions m and n, reverse in groups of k, and detect a cycle with Floyd's tortoise and hare.
Candidate Response Strategy & Interview Tips
- Start with a concise one-sentence summary: Deliver a direct, confident answer first before expanding into nuances.
- Demonstrate real-world trade-offs: Discuss where this approach excels and when you would avoid it in production systems.
- Discuss complexity & edge cases: Proactively explain time/space complexity or boundary conditions (null values, scale limits).
- Prepare for interviewer follow-ups: Technical hiring panels frequently probe deeper into concurrency, backward compatibility, or alternative libraries.