所有子字符串中的元音

/*
 * Solution using Java Streams
 * 
 * The approach is similar, but we use Java Streams to iterate over the characters.
 * We filter out non-vowels, map the indices to the count of substrings they can form, and sum them.
 */

import java.util.stream.IntStream;

public class VowelSubstringCountStream {
    public static long countVowels(String word) {
        int n = word.length();
        return IntStream.range(0, n)
                .filter(i -> isVowel(word.charAt(i)))
                .mapToLong(i -> (long) (i + 1) * (n - i))
                .sum();
    }

    private static boolean isVowel(char c) {
        return "aeiou".indexOf(c) >= 0;
    }

    public static void main(String[] args) {
        System.out.println(countVowels("aba"));  // Output: 6
        System.out.println(countVowels("abc"));  // Output: 3
        System.out.println(countVowels("ltcd")); // Output: 0
        System.out.println(countVowels("noosabasboosa")); // Output: 237
    }
}