he-016

# HumanEval/16

Implement a file **`solution.py`** that completes the function below. Keep the given name and signature; your file must define it at module level.

```python


def count_distinct_characters(string: str) -> int:
    """ Given a string, find out how many distinct characters (regardless of case) does it consist of
    >>> count_distinct_characters('xyzXYZ')
    3
    >>> count_distinct_characters('Jerry')
    4
    """
```

<!-- imported from OpenAI HumanEval (HumanEval/16) -->

# Auto-generated from OpenAI HumanEval HumanEval/16. Do not edit by hand.
from solution import *  # noqa: F401,F403 (prompt helpers may be referenced by tests)
from solution import count_distinct_characters as candidate

METADATA = {
    'author': 'jt',
    'dataset': 'test'
}


def check(candidate):
    assert candidate('') == 0
    assert candidate('abcde') == 5
    assert candidate('abcde' + 'cade' + 'CADE') == 5
    assert candidate('aaaaAAAAaaaa') == 1
    assert candidate('Jerry jERRY JeRRRY') == 5


def test_he_016():
    check(candidate)

You are an expert programmer. Solve the task exactly as specified. Output your solution as fenced code blocks using the required file name(s) and the exact function/type signatures requested. Prefer correctness; do not include prose outside code unless asked.

```python
def count_distinct_characters(string: str) -> int:
    """ Given a string, find out how many distinct characters (regardless of case) does it consist of
    >>> count_distinct_characters('xyzXYZ')
    3
    >>> count_distinct_characters('Jerry')
    4
    """
    return len(set(string.lower()))
```

The task is to implement a function `count_distinct_characters` that counts the number of distinct characters in a string, regardless of case.

Looking at the examples:
- `count_distinct_characters('xyzXYZ')` returns 3 (x, y, z - case insensitive)
- `count_distinct_characters('Jerry')` returns 4 (J, e, r, r, y - but J and j are the same, so J, e, r, y = 4 distinct characters)

So I need to:
1. Convert all characters to the same case (either upper or lower)
2. Count the unique characters

Let me write the solution:

```python
def count_distinct_characters(string: str) -> int:
    """ Given a string, find out how many distinct characters (regardless of case) does it consist of
    >>> count_distinct_characters('xyzXYZ')
    3
    >>> count_distinct_characters('Jerry')
    4
    """
    return len(set(string.lower()))
```

This should work:
- For 'xyzXYZ': lower() gives 'xyzxyz', set gives {'x', 'y', 'z'}, len is 3
- For 'Jerry': lower() gives 'jerry', set gives {'j', 'e', 'r', 'y'}, len is 4

This is a simple and correct solution.