Kebab Case a Phrase

Convert any phrase into a URL-friendly kebab-case string.

strings case-conversion regex lowercase

Write a function `to_kebab_case(s: str) -> str` that takes a string `s` and returns a URL-friendly kebab-case version.

**Rules:**
- Convert the entire string to lowercase.
- Replace any sequence of non-alphanumeric characters (spaces, punctuation, symbols) with a single hyphen `-`.
- Split camelCase boundaries: insert a hyphen between a lowercase letter and an uppercase letter (e.g., `camelCase` -> `camel-case`).
- Remove leading and trailing hyphens.
- If the result is empty after cleaning, return an empty string.

**Examples:**
- `"Hello World"` -> `"hello-world"`
- `"Hello, World!"` -> `"hello-world"`
- `"camelCase"` -> `"camel-case"`
- `"--foo--"` -> `"foo"`

**Your implementation must be iterative and use only the standard library.**

Constraints

- `0 <= len(s) <= 1000`
- The input may contain any Unicode characters, but only ASCII letters and digits are considered alphanumeric for the purpose of kebab-casing.
- Time complexity O(n), where n is the length of the string.

Example

>>> to_kebab_case("Hello World")
'hello-world'
>>> to_kebab_case("camelCase")
'camel-case'
>>> to_kebab_case("---strip--me---")
'strip-me'
>>> to_kebab_case("")
''

10 points ~15 min

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Hints

First handle camelCase by inserting a hyphen before each uppercase letter that follows a lowercase letter.

Then use a regex or manual scan to replace any run of non-alphanumeric characters with a single hyphen.

Finally, strip leading/trailing hyphens and lower everything.

Don't forget to return an empty string if no alphanumeric characters remain.

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