LeetCode每日一题——2586. Count the Number of Vowel Strings in Range

一、题目

You are given a 0-indexed array of string words and two integers left and right.

A string is called a vowel string if it starts with a vowel character and ends with a vowel character where vowel characters are ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’.

Return the number of vowel strings words[i] where i belongs to the inclusive range [left, right].

Example 1:

Input: words = [“are”,“amy”,“u”], left = 0, right = 2
Output: 2
Explanation:

• “are” is a vowel string because it starts with ‘a’ and ends with ‘e’.
• “amy” is not a vowel string because it does not end with a vowel.
• “u” is a vowel string because it starts with ‘u’ and ends with ‘u’.
  The number of vowel strings in the mentioned range is 2.
  Example 2:

Input: words = [“hey”,“aeo”,“mu”,“ooo”,“artro”], left = 1, right = 4
Output: 3
Explanation:

• “aeo” is a vowel string because it starts with ‘a’ and ends with ‘o’.
• “mu” is not a vowel string because it does not start with a vowel.
• “ooo” is a vowel string because it starts with ‘o’ and ends with ‘o’.
• “artro” is a vowel string because it starts with ‘a’ and ends with ‘o’.
  The number of vowel strings in the mentioned range is 3.

Constraints:

1 <= words.length <= 1000
1 <= words[i].length <= 10
words[i] consists of only lowercase English letters.
0 <= left <= right < words.length

二、题解

class Solution {
public:
    int vowelStrings(vector<string>& words, int left, int right) {
        unordered_set<char> set = {'a','e','i','o','u'};
        int res = 0;
        for(int i = left;i <= right;i++){
            char front = words[i][0];
            char back = words[i].back();
            if(set.count(front) && set.count(back)) res++;
        }
        return res;
    }
};