Write a Python function called `find_substrings(s, k)` that takes a string `s` and an integer `k` as input and returns a list of all unique substrings of length k that can be formed from the characters in the string.

You need to ensure that the function has the following signature:
```
def find_substrings(s: str, k: int) -> List[str]:
```

For example, if the input string `s` is "abcde" and the integer `k` is 3, the function should return the list `["abc", "bcd", "cde"]`.
user
Sure, here's the Python function `find_substrings` that does what you're asking:

```python
def find_substrings(s, k):
    # initialize an empty list to store unique substrings
    substrings = []

    # the length of the current substring being formed
    current_length = 1

    # starting index and ending index of the current substring
    start_idx, end_idx = 0, 0

    # loop over all possible substring starting indexes
    for I in range(len(s)):

        # ending index is always current length plus the starting index
        end_idx = current_length + I

        # check if the substring is unique and of length k
        if I != start_idx and end_idx < len(s) and current_length == k:
            substring = s[start_idx:end_idx]
            if substring not in substrings:
                substrings.append(substring)

        # update the starting index and current length
        start_idx += 1
        current_length += 1

    return substrings
```

Here's how this function works:

1. It initializes an empty list `substrings` to store the unique substrings.

2. `current_length` is initialized to 1 because the first substring is of length 1.

3. It loops over all possible starting indices.

4. For each starting index `i`:

   - The ending index is `current_length + i` because the length of the substring is `current_length`.

   - It checks if the substring is still unique and of length `k`, meaning it's unique from the previous substrings, then it's appended to the list.

5. The starting index `start_idx` and current length `current_length` is updated.

6. Finally, it returns the list.
assistant
Write a Python function called `find_substrings(s, k)` that takes a string `s` and an integer `k` as input and returns a list of all unique substrings of length k that can be formed from the characters in the string.

You need to ensure that the function has the following signature:
```
def find_substrings(s: str, k: int) -> List[str]:
```

For example, if the input string `s` is "abcde" and the integer `k` is 3, the function should return the list `["abc", "bcd", "cde"]`.
user
Sure, here is a Python function that meets your requirements:

```python
from typing import List

def find_substrings(s: str, k: int) -> List[str]:
    if k > len(s):
        return []
    else:
        return [s[i:i+k] for i in range(len(s) - k + 1)]
```

This function first checks if the length of the substring `k` is greater than the length of the string `s`. If it is, the function returns an empty list. Otherwise, it uses a list comprehension to generate all possible substrings of length `k` from the string `s` and returns this list. The substrings are generated by slicing the string `s` from index `i` to `i+k` for all valid indices `i`.
assistant