[LeetCode]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.

[LeetCode Source]

思路：判断是否回文，最简单的想法就是一个指针指首部，一个指尾部。依次比较判断。

这个题目比较特殊的是要跳过无效的字母，写一个isChar()的判断方法即可。

class Solution {
public:
    bool isPalindrome(string s) {
        int length = s.size();
        if(length<=1)
            return true;
        int begin = 0;
        int end = length-1;
        while(begin<end){
            while(begin<end&&!isChar(s[begin])){
                begin++;
            }
            while(begin<end&&!isChar(s[end])){
                end--;
            }
            if(tolower(s[begin++])!=tolower(s[end--]))
                return false;
        }
        return true;
    }
    bool isChar(char c){
        if('a'<=c&&c<='z'||'0'<=c&&c<='9'||'A'<=c&&c<='Z')
            return true;
        else 
            return false;
    }
};