using System;

public class Program

{

    private void TestFunction(string str, int k)

    {

        foreach(char s in str)

        {}

    }

    public static void Main()

    {

        Console.WriteLine("Hello World");

    }

}

​

//Find all substrings containing exactly `k` distinct characters

​

//Input: str = abcbd, k = 3

//Output: [abc, abcb, bcbd, cbd]

//Input: str = abcadce, k = 4

//Output: [abcad, abcadc, bcad, bcadc, cadce, adce]

//Input: str = aa, k = 1

//Output: [a, aa]