Why should you care?

O(n) hash solutions beat O(n²) scans.

See it live — copy this example

Run snippets in a .NET console app, LINQPad, or https://dotnetfiddle.net. Write Big O above every solution.

var map = new Dictionary<int, int>();
var set = new HashSet<int>();
// Caching Lookups

What happened?

• Define the key carefully; handle missing keys with TryGetValue.
• Follow the steps below — typing the code yourself is the fastest way to learn.

Practice next

1. Type the snippet in a C# console or LINQPad.
2. Write Big O on top of your solution.
3. Test empty / single-element edge cases.
4. Add a failing test then fix it.
5. Rename variables to domain words.

Remember

You can code a small C# example for Caching Lookups. You know the complexity class. You tested at least one edge case.

Caching Lookups drill

AlgoVerse interview prompt on caching lookups.

Outcome: You recognize the pattern and ship a correct C# sketch.