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Formatted question description: https://leetcode.ca/all/2255.html

2255. Count Prefixes of a Given String (Easy)

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.

Related Topics:
Array, String

Similar Questions:

Solution 1.

// OJ: https://leetcode.com/problems/count-prefixes-of-a-given-string/
// Time: O(NS) where `N` is length of `A`, and `S` is length of `s`
// Space: O(S)
class Solution {
    int countPrefixes(vector<string>& A, string s) {
        int ans = 0;
        for (auto &w : A) {
            ans += !s.compare(0, w.size(), w);
        return ans;

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