Valid Palindrome

class Solution {public:    char clearChar(char input)    {        if((input>='a')&&(input<='z'))        {            return input;        }        if((input>='0')&&(input<='9'))        {            return input;        }        if((input>='A')&&(input<='Z'))        {            return input+('a'-'A');        }        return 0;    }    bool isPalindrome(string s) {        int n=s.size();        int index1=0;        int index2=n-1;        if(index1>=index2)        {            return true;        }        while(index1<index2)        {            char a=0;            while((index1<n)&&(a=clearChar(s[index1]))==0)            {                index1++;            }            char b=0;            while((index2>=0)&&(b=clearChar(s[index2]))==0)            {                index2--;            }            if((a!=0)&&(b!=0))            {                if(a!=b)                {                    return false;                }                index1++;                index2--;               }        }        return true;    }};