C# interview questions

Write a private async Task<int> helper that returns its argument doubled, then implement the public entry point SumDoubled(List<int> numbers). SumDoubled itself is synchronous: it must start one helper task per number, await them all with

An unreliable async operation is scripted by outcomes: attempt number i (zero-based) succeeds when outcomes[i] is true. Implement AttemptsUntilSuccess(List<bool> outcomes, int maxAttempts).

What does await actually do when you hit it? Does it start a new thread?

Why is async void almost always a mistake, and what is the one place it is legitimate?

Implement GroupByLength(List<string> words) returning a Dictionary<int, int> from word length to how many words have that length. Ignore null and empty strings.

Implement AboveThreshold(List<int> numbers, int threshold) that returns the distinct values strictly greater than threshold, sorted ascending, as a List<int>. Return an empty list when nothing qualifies.