125_valid_palindrome

Leetcode 125: Valid Palindrome
Detailed video explanation: https://youtu.be/028pTf2kBFI
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C++:
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class Solution {
public:
    bool isPalindrome(string s) {
        if(s.length() <= 1) return true;
        int st = 0, en = s.length()-1;
        while(st < en){
            while(st < en && !isalnum(s[st])) st++;
            while(st < en && !isalnum(s[en])) en--;
            if(st < en && tolower(s[st]) != tolower(s[en])) return false;
            st++;
            en--;
        }
        return true;
    }
};


Java:
----
class Solution {
    public boolean isPalindrome(String s) {
        if(s.length() <= 1) return true;
        int st = 0, en = s.length()-1;
        while(st < en){
            while(st < en && !Character.isLetterOrDigit(s.charAt(st))) st++;
            while(st < en && !Character.isLetterOrDigit(s.charAt(en))) en--;
            if(st < en && Character.toLowerCase(s.charAt(st)) != Character.toLowerCase(s.charAt(en))) return false;
            st++;
            en--;
        }
        return true;
    }
}


Python3:
--------
class Solution:
    def isPalindrome(self, s: str) -> bool:
        if len(s) <= 1: return True
        st, en = 0, len(s)-1
        while st < en:
            while st < en and not s[st].isalnum(): st += 1
            while st < en and not s[en].isalnum(): en -= 1
            if st < en and s[st].lower() != s[en].lower(): return False
            st, en = st+1, en-1
        return True