Given a string `s` and an array of strings `words`, determine whether `s` is a prefix string of `words`.

A string `s` is a prefix string of `words` if `s` can be made by concatenating the first `k` strings in `words` for some positive `k` no larger than `words.length`.

Return `true` if `s` is a prefix string of `words`, or `false` otherwise.

Example 1:

    Input: s = "iloveleetcode", words = ["i","love","leetcode","apples"]
    Output: true
    Explanation:
    s can be made by concatenating "i", "love", and "leetcode" together.

Example 2:

    Input: s = "iloveleetcode", words = ["apples","i","love","leetcode"]
    Output: false
    Explanation:
    It is impossible to make s using a prefix of arr.

Constraints:

- `1 <= words.length <= 100`
- `1 <= words[i].length <= 20`
- `1 <= s.length <= 1000`
- `words[i]` and `s` consist of only lowercase English letters.