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.

解題

func countPrefixes(words []string, s string) int {
    m := make(map[string]bool)
    ans := 0
    
    for i:=len(s); i>0; i-- {
        m[s[:i]] = true
    }
    
    for _, word := range words {
        if m[word] { ans++ }
    }
    
    return ans
}