leetcode[125]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.

class Solution {
public:
bool isValid(char c)
{
    if((c>='a'&&c<='z')||(c>='A'&&c<='Z')||(c>='0'&&c<='9'))return true;
    return false;
}
bool isSame(char c1, char c2)
{
    if(c1>='0'&&c1<='9')return c1==c2;
    if((c1>='A'&&c1<='Z'))return (c1==c2)||(c1==c2-32);
    if(c1>='a'&&c1<='z')return (c1==c2)||(c1==c2+32);
}
    bool isPalindrome(string s) {
        if(s.empty()||s.size()==1)return true;
        int n=s.size();
        int i=0,j=n-1;
        for(;i<n&&j>=0&&i<=j;)
        {
//            if(i==j)return true;
            while(!isValid(s[i]))i++;
            while(!isValid(s[j]))j--;
            if(i==j||i>j)return true;
            if(!isSame(s[i],s[j]))return false;
            i++;
            j--;
        }
        if(i==j||i>j)return true;
        return false;
    }
};