leetcode题解：Valid Palindrome（判断回文）

题目：

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.

说明：

1）注意两点：a、判断满足条件的字符  b、大写变小写（本题认为不区分大小写）

2）字符串为空则true

实现：

 class Solution {
 public:
         bool isPalindrome(string s) {
             if(s.empty()) return true;
             int len=strlen(s.c_str());
             int i=;
             int j=;
             for (;i<len;i++)
             {
                 if (isChar(s[i]))//去其他符合，若有大写则大写变小写
                 {
                     s[i] = tolower(s[i]);//库函数
                     s[j++]=s[i];
                 }
             }
             s[j]='\0';
             if (s[]=='\0') return true;
             int len2=strlen(s.c_str());
             i=;
             while(i<=len2--i) //判断是否回文
             {
                 if(s[i]!=s[len2--i]) return false;
                 i++;
             }
             return true;
     }
     private:
         bool isChar(char t)//判断是否满足条件字符
         {
             if (('a' <= t&&t<='z')||('A' <= t&&t<='Z')||('' <= t&&t<=''))
            {
                return true;
            }
            else
                return false;
         }
 };