LetCode 125. 验证回文串

class Solution {
public:
    bool isPalindrome(string s) {
        if (s.length() <= 1)
            return true;
        int last = s.length() - 1;
        int first = 0;
        // 先统一转化为小写
        for(int i = 0; i < s.length(); ++i)
            s[i] = tolower(s[i]);
        while(first <= last){
            // 忽略不是字母或数字的字符
            while(!isalnum(s[first]) && first <= last) ++first;
            while(!isalnum(s[last]) && first <= last) --last;
            if (first > last)
                return true;
            if (s[first] != s[last])
                return false;
            ++first,--last;
        }
        return true;
    }
};

static int x=[](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();