Recursion coding problem

Problem A recursion-based coding exercise given live in the pair-programming round. The idea is straightforward but easy to get wrong in code — the interviewer probes many edge cases and expects a clean recursive formulation.

Input / Output

• Input / Output: depend on the specific prompt (typically an array or string processed recursively).

Constraints

• Handle empty input, single-element input, and deeply nested / large inputs without exceeding the recursion depth.

Example

• The interviewer walks through several inputs, including boundary cases, and expects each to produce the correct result.

Expected approach

• Define the base case(s) precisely, express the recurrence over a smaller sub-problem, and reason about correctness and recursion depth. Be ready to convert to an iterative form or add memoization if depth or repeated sub-problems become a concern.