Problem

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

Note: For the purpose of this problem, we define empty string as valid palindrome.

Example

Input: "A man, a plan, a canal: Panama"
Output: true

Input: "race a car"
Output: false

Code

static int var = [](){
    std::ios::sync_with_stdio(false);
    cin.tie(NULL);
    return 0;
}();
class Solution {
public:
    bool isPalindrome(string s) {
        int i=0;
        int j=s.size()-1;
        transform(s.begin(),s.end(),s.begin(), ::tolower);
        while(i<j){
            if(!((s[i]>='a'&&s[i]<='z') || (s[i]>='0'&&s[i]<='9'))){
                i++;
                continue;
            }
            if(!((s[j]>='a'&&s[i]<='z') || (s[j]>='0'&&s[j]<='9'))){
                j--;
                continue;
            }
            if(s[i]==s[j]){
                i++;
                j--;
                continue;
            }else{
                return false;
            }
        }
        return true;
    }
};

Result

125. Valid Palindrome.png