Valid Palindrome

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

For example,
"A man, a plan, a canal: Panama" is a palindrome.
"race a car" is not a palindrome.

Note:
Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

• 检测是不是回文

bool isAlphaOrNum(char c)    //检测是否为字母或数字
{
    if( (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z'))
        return 1;
    else
        return 0;
}
bool isPalindrome(char* s) {
    int size = strlen(s);
    int i = 0, j = size - 1;
    while(i <= j)
    {
        if(i == j)
            return true;
        if(  !isAlphaOrNum( *(s + i) ) )    //如果不是字母或数字则指针移动，同时返回while去检测是i，j位置关系
            {
                i++;
                continue;
            }
        if( !isAlphaOrNum( *(s + j) ) )    //最好while里面不要再while，很容易错
            {
                j--;
                continue;
            }
        if( *(s + i) == *(s + j) || *(s + i) - *(s + j) == 'A' - 'a' || *(s + j) - *(s + i) == 'A' - 'a')
            {
                i++;
                j--;
            }
        else
            return false;
    }
    return true;    //当输入为空时，返回为true
}