HumanEval38.lean

def decode_cyclic : Unit :=
  ()

/-!
## Prompt

```python3


def encode_cyclic(s: str):
    """
    returns encoded string by cycling groups of three characters.
    """
    # split string to groups. Each of length 3.
    groups = [s[(3 * i):min((3 * i + 3), len(s))] for i in range((len(s) + 2) // 3)]
    # cycle elements in each group. Unless group has fewer elements than 3.
    groups = [(group[1:] + group[0]) if len(group) == 3 else group for group in groups]
    return "".join(groups)


def decode_cyclic(s: str):
    """
    takes as input string encoded with encode_cyclic function. Returns decoded string.
    """
```

## Canonical solution

```python3
    return encode_cyclic(encode_cyclic(s))
```

## Tests

```python3


METADATA = {}


def check(candidate):
    from random import randint, choice
    import string

    letters = string.ascii_lowercase
    for _ in range(100):
        str = ''.join(choice(letters) for i in range(randint(10, 20)))
        encoded_str = encode_cyclic(str)
        assert candidate(encoded_str) == str

```
-/