【leetcode】Valid Palindrome

class Solution {
public:

    bool check1(char ch)//当ch在'a'-'z'之间时，返回true
    {
        if(ch>='a'&&ch<='z')
            return true;
        return false;    
    }
    
    bool check2(char ch)//当ch在'A'-'Z'之间时，返回true
    {
        if(ch>='A'&&ch<='Z')
            return true;
        return false;
    }

    bool check3(char ch)//当ch在'0'-'9'之间时，返回true
    {
        if(ch>='0'&&ch<='9')
            return true;
        return false;    
    }

    bool isPalindrome(string s) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        if(s.size()==0||s.size()==1)
            return true;
        
        int sta=0,end=s.size()-1;
        while(sta<end)
        {
            while(check1(s[sta])==false&&check2(s[sta])==false&&check3(s[sta])==false)
            {
                sta++;
                if(sta>=s.length())//溢出
                    break;
            }
                
            while(check1(s[end])==false&&check2(s[end])==false&&check3(s[end])==false)
            {
                end--;
                if(end<0)//溢出
                    break;
            }
             
            if(check2(s[sta]))//大写转小写
                s[sta]=s[sta]-'A'+'a';
            if(check2(s[end]))
                s[end]=s[end]-'A'+'a';
            
            if(sta<end&&s[sta]!=s[end])
                return false;
            sta++;
            end--;
        }
        return true;
    }
};