反转字符串中的元音字符

345 Reverse Vowels of a String (Easy)

Leetcode / 力扣

Given s = "leetcode", return "leotcede".

使用双指针，一个从头到尾遍历，一个从尾到头遍历，当两个指针都遍历到元音字母时，将他们交换。

private final static HashSet<Character> vowels = new HashSet<>(
        Arrays.asList('a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U'));

public String reverseVowels(String s) {
    if (s == null) return null;
    int i = 0, j = s.length() - 1;
    char[] result = new char[s.length()];
    while (i <= j) {
        char ci = s.charAt(i);
        char cj = s.charAt(j);
        if (!vowels.contains(ci)) {
            result[i++] = ci;
        } else if (!vowels.contains(cj)) {
            result[j--] = cj;
        } else {
            result[i++] = cj;
            result[j--] = ci;
        }
    }
    return new String(result);
}