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.