How do you reverse a linked list (iterative and recursive)?

Short answer: Iterative: three pointers prev, curr, next. Flip curr.next to prev and advance. Recursive: reverse the rest, then point head.next.next = head and head.next = null. Iterative is usually preferred in interviews for O(1) stack space.

Complexity

Time O(n). Iterative space O(1); recursive space O(n) call stack.

Edge cases to mention

• Empty list
• Single node
• Cycle (clarify — usually assume none)

Common follow-ups

• Reverse nodes in k-group
• Reverse between left and right

Draw 3 nodes on the whiteboard before coding — it prevents pointer bugs.