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.两个指针问题*/#include <iostream>#include <string>using namespace std;class Solution {public:    bool isPalindrome(string s) {        int left=0,right=s.size()-1;        while(left<right)        {            while(left<right && isalnum(s[left]) == false)                left++;            while(left<right && isalnum(s[right]) == false )                right--;            if(left>=right) return true;            if(toupper(s[left]) != toupper(s[right]))                return false;            left++,right--;        }        return true;    }};int main(){    Solution mys;    string s="canal: Panama";    cout<<mys.isPalindrome(s)<<endl;    return 0;}