Common Code Patterns

Experienced programmers don't solve each problem from scratch. They recognize patterns and apply proven approaches. Here are essential patterns you'll use constantly. The Transform Pattern Convert each element into a new form. Use when you need to change every item in a collection. The Reduce Pattern Combine all elements into a single value. Use for totals, products, finding min/max, or building composite results. The Two-Pass Pattern Sometimes you need information from the entire collection before processing. Make one pass to gather data, another to use it. The transform, reduce, and two-pass patterns are building blocks that combine naturally. Real-world solutions often chain them: reduce the data to compute an aggregate, then transform every element relative to that aggregate. List comp

About This Interactive Section

This section is part of the Problem Solving: Intermediate 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.

How DataDriven Lessons Work

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.