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>();
// Two Sum with Dictionary

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 Two Sum with Dictionary. You know the complexity class. You tested at least one edge case.

Two Sum with Dictionary drill

AlgoVerse interview prompt on two sum with dictionary.

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