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.

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Example 1:

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

Example 2:

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

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Constraints:

• 1 <= words.length <= 100

• 1 <= words[i].length <= 20

• 1 <= s.length <= 1000

• words[i]?and?s?consist of only lowercase English letters.

Runtime:?3 ms, faster than?30.70%?of?Java?online submissions for?Check If String Is a Prefix of Array.

Memory Usage:?43.9 MB, less than?6.17%?of?Java?online submissions for?Check If String Is a Prefix of Array.

用stringbuilder 遍歷數(shù)組的字符，每次跟選定的字符串比對是否一樣，即可確認prefix是不是字符串s了。