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2255 - Count Prefixes of a Given String (Easy)

https://leetcode.com/problems/count-prefixes-of-a-given-string/

Problem Statement​

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
Explanation:
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
Explanation:
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.

Constraints:

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

Approach 1: STL​

Written by @wingkwong
class Solution {
public:
    int countPrefixes(vector<string>& words, string s) {
        int ans = 0;
        // if it returns index 0, then it means t is the prefix of s 
        for (auto& t : words) ans += s.find(t) == 0;
        return ans;
    }
};