125.验证回文串

https://leetcode-cn.com/problems/valid-palindrome/

public boolean isPalindrome(String s) {
    if (s.length() == 0) {
        return true;
    }
    char[] str = s.toCharArray();
    int L = 0;
    int R = s.length() - 1;
    while (L < R) {
        while (L < R && !Character.isLetterOrDigit(str[L])) {
            ++L;
        }
        while (L < R && !Character.isLetterOrDigit(str[R])) {
            --R;
        }
        if (Character.toLowerCase(str[L]) != Character.toLowerCase(str[R])) {
            return false;
        }
        ++L;
        --R;
    }
    return true;
}

另一个版本，不用Character类

public static boolean isPalindrome(String s) {
        if (s == null || s.length() == 0) {
            return true;
        }
        char[] str = s.toCharArray();
        int L = 0;
        int R = str.length - 1;
        while (L < R) {
            if (validChar(str[L]) && validChar(str[R])) {
                if (!equal(str[L], str[R])) {
                    return false;
                }
                L++;
                R--;
            } else {
                L += validChar(str[L]) ? 0 : 1;
                R -= validChar(str[R]) ? 0 : 1;
            }
        }
        return true;
    }
    public static boolean validChar(char c) {
        return isLetter(c) || isNumber(c);
    }
    public static boolean equal(char c1, char c2) {
        if (isNumber(c1) || isNumber(c2)) {
            return c1 == c2;
        }
        return (c1 == c2) || (Math.max(c1, c2) - Math.min(c1, c2) == 32);
    }
    public static boolean isLetter(char c) {
        return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
    }
    public static boolean isNumber(char c) {
        return (c >= '0' && c <= '9');
    }