C# hackerrank interview question

I am looking to hire a freelancer to solve a hard interview question for a C# role. The ideal candidate should have experience in the field, as well as general knowledge of C#. The question should focus on general C# knowledge, rather than specific topics or areas such as data structures or algorithms. The successful freelancer's application should include information about past work and detailed project proposals.

I have 90 min to answer the question but I want to be able to understand your answer as well. Not looking for a chatgpt answer. Have good pseudocode