What is the space complexity of a recursive reverse of a linked list?

• A. O(log n)
• B. O(n^2)
• C. O(n) due to recursion stack.
• D. O(1) constant space.

Answer: (C)

Recursive reversal of a singly linked list hinges on how deep the function calls go. Each time you reverse the rest of the list, you make another recursive call, so for a list with n nodes the recursion can reach n levels before hitting the base case. That means there are n active stack frames at the deepest point, and each frame uses a small, constant amount of memory for parameters and control data. The peak extra memory, brought by these stacked frames, grows linearly with the number of nodes, giving an auxiliary space complexity of O(n).

This contrasts with an iterative in-place reverse, which can achieve O(1) extra space because it uses a constant number of pointers regardless of list size. The other options—logarithmic or quadratic growth—don’t match the linear depth of the recursion in a linked-list structure.