You are given a list of strings, where each string represents a distinct country. Your task is to write a function `unite_countries` that takes in the list of countries and returns a single string representing the united form of those countries.

The united form of the countries is obtained as follows:
- If there is only one country in the list, the united form is simply that country.
- If there are two countries in the list, the united form is formed by concatenating the two country names with a hyphen in between.
- If there are more than two countries in the list, the united form is formed by concatenating all the country names with commas and a space between each country name, and ending with the word "and" followed by the last country name.

Write a function `unite_countries(countries: List[str]) -> str` to solve the problem.

**Examples**
Example 1:
```
Input:
countries = ["United States", "Canada", "Mexico"]

Output:
"United States, Canada, and Mexico"
```

Example 2:
```
Input:
countries = ["Italy"]

Output:
"Italy"
```

Example 3:
```
Input:
countries = ["Japan", "South Korea"]

Output:
"Japan-South Korea"
```

Note:
- The input list will always contain at least one string.
- The country names are case-sensitive.
user
Sure, I can help you with that task. Here's a Python function `unite_countries` that meets your requirements:

```python
def unite_countries(countries):
    # If there's only one country, return it
    if len(countries) == 1:
        return countries[0]

    # If there are two countries, concatenate them with a hyphen
    elif len(countries) == 2:
        return countries[0] + '-' + countries[1]

    # Otherwise, concatenate all countries with commas and 'and' at the end
    else:
        return ', '.join(countries) + ', and ' + countries[-1]
```

This function first checks if there's only one country, in which case it returns that country. If there are two countries, it concatenates them with a hyphen. Otherwise, it concatenates all countries with commas and 'and' at the end.

Note: This function assumes that the input list is not empty. You may want to add an additional check for that.
assistant
You are given a list of strings, where each string represents a distinct country. Your task is to write a function `unite_countries` that takes in the list of countries and returns a single string representing the united form of those countries.

The united form of the countries is obtained as follows:
- If there is only one country in the list, the united form is simply that country.
- If there are two countries in the list, the united form is formed by concatenating the two country names with a hyphen in between.
- If there are more than two countries in the list, the united form is formed by concatenating all the country names with commas and a space between each country name, and ending with the word "and" followed by the last country name.

Write a function `unite_countries(countries: List[str]) -> str` to solve the problem.

**Examples**
Example 1:
```
Input:
countries = ["United States", "Canada", "Mexico"]

Output:
"United States, Canada, and Mexico"
```

Example 2:
```
Input:
countries = ["Italy"]

Output:
"Italy"
```

Example 3:
```
Input:
countries = ["Japan", "South Korea"]

Output:
"Japan-South Korea"
```

Note:
- The input list will always contain at least one string.
- The country names are case-sensitive.
user
Sure, I can help you write the function `unite_countries` in Python. Here's how you can do it:

```python
def unite_countries(countries: List[str]) -> str:
    if len(countries) == 1:
        return countries[0]
    elif len(countries) == 2:
        return countries[0] + '-' + countries[1]
    else:
        united_countries = ', '.join(countries[:-1]) + ', and ' + countries[-1]
        return united_countries
```

In this function, we first check the length of the input list `countries`. If it's 1, we simply return the first (and only) element of the list. If it's 2, we return the two country names concatenated with a hyphen. If it's more than 2, we join all but the last country name with a comma and a space, then add 'and' followed by the last country name.

This function should work correctly for all the examples you provided. Please ensure that you have the `typing` module imported in your Python environment for the `List[str]` notation to work. If it's not available, you can simply use a regular list notation (`[]`) for the input and output types.
assistant