Flatten deeply with pattern matching in C#
C# interview exercise on Collections & LINQ, difficulty 2 of 3. Solve it in the editor beside a worked example, or cold in Interview mode with the example hidden; the tests run the moment you do.
A list of object can hold ints and further lists of object, nested to any depth. Write FlattenDeep(items) that returns every int, depth-first. `is` with a type pattern tests the type and names the value in one step.
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Interview mode hides the example: solve it from memory, without the hint or the solution, and it counts as solved cold. Progress is saved in your browser, and in your account if you sign in.