2255

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
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.

Related Topics:
Array, String

Similar Questions:

• Check If a Word Occurs As a Prefix of Any Word in a Sentence (Easy)
• Check If String Is a Prefix of Array (Easy)
• Counting Words With a Given Prefix (Easy)

Solution 1.

// OJ: https://leetcode.com/problems/count-prefixes-of-a-given-string/
// Author: github.com/lzl124631x
// Time: O(NS) where `N` is length of `A`, and `S` is length of `s`
// Space: O(S)
class Solution {
public:
    int countPrefixes(vector<string>& A, string s) {
        int ans = 0;
        for (auto &w : A) {
            ans += !s.compare(0, w.size(), w);
        }
        return ans;
    }
};