【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;    }};