How to add a new challange?

Fork this project if you haven't done so
Determine how difficult the challenge is. There are 3 levels: basic, intermediate, and advanced.
Create a new directory under challenges/. The new directory's name should follow the pattern [basic|intermediate|advanced]-name.

For example, say you want to add a new challenge about Protocols. Since this is an advanced topic, you may name the directory advanced-protocol.
Put a question.py in the new directory. Here's an example:
```
"""
TODO:

foo should accept a dict argument, both keys and values are string.
"""

def foo(x):
    pass

def should_pass():
    foo({"foo": "bar"})

def should_fail():
    foo({"foo": 1})
```
You want to include several things in question.py
- Describe the challenge, make sure people understand what they need to accomplish (the TODO: part)
- Add two functions should_pass and should_fail as test cases. The function names are mandatory. With correct code, should_pass should pass type check, and should_fail should fail type check.
Using the above challenge as an example, the correct answer is def foo(x: dict[str: str]): pass.

This will pass type check:
```
def foo(x: dict[str: str]):
    pass

def should_pass():
    foo({"foo": "bar"})
```
This will fail type check
```
def foo(x: dict[str: str]):
    pass

def should_fail():
    foo({"foo": 1})
```
Test with mypy to make sure your new challenge works as expected.
Create a Pull Request.

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