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Abhishek Chaudhary
Abhishek Chaudhary

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Count Prefixes of a Given String

You are given a string array words and a string s, where words[i] and s comprise only of lowercase English letters.

Return the number of strings in words that are a prefix of s.

A prefix of a string is a substring that occurs at the beginning of the string. A substring is a contiguous sequence of characters within a string.

Example 1:

Input: words = ["a","b","c","ab","bc","abc"], s = "abc"
Output: 3
The strings in words which are a prefix of s = "abc" are:
"a", "ab", and "abc".
Thus the number of strings in words which are a prefix of s is 3.

Example 2:

Input: words = ["a","a"], s = "aa"
Output: 2
Both of the strings are a prefix of s.
Note that the same string can occur multiple times in words, and it should be counted each time.


  • 1 <= words.length <= 1000
  • 1 <= words[i].length, s.length <= 10
  • words[i] and s consist of lowercase English letters only.


class Solution:
    def countPrefixes(self, words: List[str], s: str) -> int:
        n = len(s)
        prefixes = set()
        for i in range(1, n + 1):
        ctr = 0
        for w in words:
            if w in prefixes:
                ctr += 1
        return ctr
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