2586. Count the Number of Vowel Strings in Range 

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class Solution {
    private static final Set<Character> VOWEL_CHAR_SETS = new HashSet<>(Arrays.asList('a', 'e', 'i', 'o', 'u'));

    public int vowelStrings(String[] words, int left, int right) {
        int count = 0;
        for (int i = left; i <= right; i++) {
            if (ifVowelString(words[i])) {
                count++;
            }
        }
        return count;
    }

    private boolean ifVowelString(String word) {
        return VOWEL_CHAR_SETS.contains(word.charAt(0)) && VOWEL_CHAR_SETS.contains(word.charAt(word.length() - 1));
    }
}

References

2586. Count the Number of Vowel Strings in Range