统计范围内的元音字符串数

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

// 思路：
// 1. 使用 Java Stream 处理从 left 到 right 范围内的 words 数组。
// 2. 过滤出以元音字母开头并以元音字母结尾的字符串。
// 3. 统计满足条件的字符串数量并返回。

import java.util.Arrays;

public class VowelStringCounterStream {
    public static int countVowelStrings(String[] words, int left, int right) {
        String vowels = "aeiou";
        return (int) Arrays.stream(words, left, right + 1)
                .filter(word -> vowels.indexOf(word.charAt(0)) != -1 && vowels.indexOf(word.charAt(word.length() - 1)) != -1)
                .count();
    }
    public static void main(String[] args) {
        String[] words1 = {"are", "amy", "u"};
        int left1 = 0, right1 = 2;
        System.out.println(countVowelStrings(words1, left1, right1)); // 输出：2

        String[] words2 = {"hey", "aeo", "mu", "ooo", "artro"};
        int left2 = 1, right2 = 4;
        System.out.println(countVowelStrings(words2, left2, right2)); // 输出：3
    }
}

这个题解使用了列表推导和 Python 的内置函数 sum 来统计元音字符串的数量。首先，对于 words 数组中的索引从 left 到 right 的每个元素（即字符串），检查该字符串的第一个字符和最后一个字符是否都是元音字母（'a', 'e', 'i', 'o', 'u'）。如果两个条件都满足，则该字符串被认为是元音字符串。列表推导会为每个元音字符串生成 True，非元音字符串生成 False。最后，使用 sum 函数计算列表中 True 的总数，即为所求的元音字符串数量。

O(n)

O(n)