【LeetCode】125. Valid Palindrome

题解：用两指针即可

bool isPalindrome(string s) {    int len=s.size();    int lt=0,rt=len-1;    while(lt<rt)    {       while(isalnum(s[lt])==false&<<rt)lt++;       while(isalnum(s[rt])==false&<<rt)rt--;       if(toupper(s[lt])!=toupper(s[rt]))return false;             lt++;rt--;                }    return true;}