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;
    }
};