2255. Count Prefixes of a Given String

Problem

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.

Solution (Java)

class Solution {
    public int countPrefixes(String[] words, String s) {
        int count = 0;
        for (String str : words) {
            if (s.indexOf(str) == 0) {
                ++count;
            }
        }
        return count;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).