HumanEval78.lean

def hex_key : Unit :=
  ()

/-!
## Prompt

```python3

def hex_key(num):
    """You have been tasked to write a function that receives 
    a hexadecimal number as a string and counts the number of hexadecimal 
    digits that are primes (prime number, or a prime, is a natural number 
    greater than 1 that is not a product of two smaller natural numbers).
    Hexadecimal digits are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F.
    Prime numbers are 2, 3, 5, 7, 11, 13, 17,...
    So you have to determine a number of the following digits: 2, 3, 5, 7, 
    B (=decimal 11), D (=decimal 13).
    Note: you may assume the input is always correct or empty string, 
    and symbols A,B,C,D,E,F are always uppercase.
    Examples:
    For num = "AB" the output should be 1.
    For num = "1077E" the output should be 2.
    For num = "ABED1A33" the output should be 4.
    For num = "123456789ABCDEF0" the output should be 6.
    For num = "2020" the output should be 2.
    """
```

## Canonical solution

```python3
    primes = ('2', '3', '5', '7', 'B', 'D')
    total = 0
    for i in range(0, len(num)):
        if num[i] in primes:
            total += 1
    return total
```

## Tests

```python3
def check(candidate):

    # Check some simple cases
    assert candidate("AB") == 1, "First test error: " + str(candidate("AB"))      
    assert candidate("1077E") == 2, "Second test error: " + str(candidate("1077E"))  
    assert candidate("ABED1A33") == 4, "Third test error: " + str(candidate("ABED1A33"))      
    assert candidate("2020") == 2, "Fourth test error: " + str(candidate("2020"))  
    assert candidate("123456789ABCDEF0") == 6, "Fifth test error: " + str(candidate("123456789ABCDEF0"))      
    assert candidate("112233445566778899AABBCCDDEEFF00") == 12, "Sixth test error: " + str(candidate("112233445566778899AABBCCDDEEFF00"))  


    # Check some edge cases that are easy to work out by hand.
    assert candidate([]) == 0

```
-/