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;

    }

};