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From first function to full system.

Answer focused software engineering questions and learn from every explanation.

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Practice workspaceTypeScript
Arrays

First unique character

Return the first character that appears only once in a string.

Input"level"
Output"v"
typescript
1const firstUnique = (text: string): string | undefined => {
2  const counts = new Map<string, number>();
3  for (const c of text) {
4    const count = counts.get(c) ?? 0;
5    counts.set(c, count + 1);
6  }
7  for (const c of text) {
8    if (counts.get(c) === 1) {
9      return c;
10    }
11  }
12};
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Read a short explanation, try the problem, and inspect an approach when you need one.

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  • 01

    Understand the idea

    Start with the concept behind the solution.

  • 02

    Work the problem

    Turn the prompt into code you can reason about.

  • 03

    Review the approach

    See what worked and where the tradeoffs sit.

Think beyond the function.

Practice the decisions behind systems that need to hold up.

System design exerciseExample brief
Design a URL shortener

What happens after a link is created?

Trace the request, choose where data lives, and explain what changes as traffic grows.

  • Request

    Validate the long URL

  • Storage

    Map a short key to a destination

  • Redirect

    Read the mapping and respond