LeetCode 125 Valid Palindrome

Input: "A man, a plan, a canal: Panama"
Output: true

Input: "race a car"
Output: false

class Solution {
public:
    bool isPalindrome(string s) {
        if(s.length()==0) return true;
        int l = s.length();
        for(int i=0,j=l-1;i<=j;i++,j--)
        {
            if(judge(s[i])&&judge(s[j]))
            {
                if(change(s[i])!=change(s[j]))
                    return false;
            }
            else if(!judge(s[i])&&judge(s[j]))
            {
                j++;
            }
            else if(judge(s[i])&&!judge(s[j]))
            {
                i--;
            }
                
        }
        
        return true;
        
    }
    int judge(char x)
    {
         if((x>='a'&&x<='z')||(x>='A'&&x<='Z')||(x>='0'&&x<='9'))
             return 1;
        else
            return 0;
            
    }
    char change(char x)
    {
        if(x>='A'&&x<='Z')
            return x+32;
        else
            
            return x;
    }
};