Recursion

Recursion is when a function calls itself. This technique is elegant for problems that can be broken into smaller versions of the same problem. While it might seem strange at first, recursion is a natural fit for many algorithms. Data engineers encounter recursion when traversing nested JSON, processing tree structures, working with file system hierarchies, or implementing divide-and-conquer algorithms. It's also a favorite topic in technical interviews. The Two Parts of Recursion Every recursive function must have two parts: a base case that stops the recursion, and a recursive case that calls itself with a smaller problem. Each call to countdown passes a smaller number. Eventually n reaches 0, hitting the base case and stopping. Without the base case, the function would call itself forev

About This Interactive Section

This section is part of the Functional Programming: Advanced lesson on DataDriven, a free data engineering interview prep platform. Each section includes explanations, worked examples, and hands-on code challenges that execute in real time. SQL queries run against a live PostgreSQL database. Python runs in a sandboxed Docker container. Data modeling problems validate against interactive schema canvases. All content is framed around what data engineering interviewers actually test at companies like Meta, Google, Amazon, Netflix, Stripe, and Databricks.

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DataDriven combines four interview rounds (SQL, Python, Data Modeling, Pipeline Architecture) with adaptive difficulty and spaced repetition. Easy problems get harder as you improve. Weak concepts resurface until you master them. Your readiness score tracks progress across every topic interviewers test. Every lesson section ends with problems you solve by writing and running real code, not by picking multiple-choice answers.