125. Valid Palindrome

双指针

class Solution {public:    bool isPalindrome(string s) {        int n=s.size();        if(n==0)            return true;        int i=0,j=n-1;        while(i<j)        {            while(!(s[i]>='a'&&s[i]<='z'||s[i]>='A'&&s[i]<='Z'||s[i]>='0'&&s[i]<='9')&&i<j)                i++;            while(!(s[j]>='a'&&s[j]<='z'||s[j]>='A'&&s[j]<='Z'||s[j]>='0'&&s[j]<='9')&&i<j)                j--;            if(s[i]>='A'&&s[i]<='Z')                s[i]=s[i]-'A'+'a';            if(s[j]>='A'&&s[j]<='Z')                s[j]=s[j]-'A'+'a';            if(s[i]!=s[j])                return false;            i++;            j--;        }        return true;    }};