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.

 

字符串为空时判断为回文，大小写不区分可确定相等，数字与字母不同。

 

1 class Solution { 2 public: 3     bool isPalindrome(string s) { 4         int n=s.length(); 5         if(n==0) return true; 6         int i=0,j=n-1; 7         while(i
     
      ='0'&&s[i]<='9')?s[i]-'0':((s[i]>='a'&&s[i]<='z')?s[i]-'a':s[i]-'A');19             right=(s[j]>='0'&&s[j]<='9')?s[j]-'0':((s[j]>='a'&&s[j]<='z')?s[j]-'a':s[j]-'A');20             leftsig=(s[i]>='0'&&s[i]<='9')?0:1;21             rightsig=(s[j]>='0'&&s[j]<='9')?0:1;22             if(left!=right||leftsig!=rightsig)23                 return false;24             i++;25             j--;26         }27         return true;28     }29     bool isCharacters(char c){30         if((c>='a'&&c<='z')||(c>='A'&&c<='Z')||(c>='0'&&c<='9'))31             return true;32         else33             return false;34     }35 };