Leetcode 125 Valid Palindrome ( C,C++,C#,Java,Javascript,Ruby)

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

Example 1:

Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.

Example 2:

Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.

Constraints:

• 1 <= s.length <= 2 * 105
• s consists only of printable ASCII characters.

//C
bool isPalindrome(char * s){
    int left=0, right=strlen(s)-1;
    while (left<right) {
        while (left<right && !isalnum(s[left]))
            left++;
        while (left<right && !isalnum(s[right]))
            right--;
        if (tolower(s[left])!=tolower(s[right]))
            return false;
        left++;
        right--;
    }
    return true;
}
//C++
class Solution {
public:
    bool isPalindrome(string s) {
        int left=0, right=s.size()-1;
        while (left<right) {
            while (left<right && !isalnum(s[left]))
                left++;
            while (left<right && !isalnum(s[right]))
                right--;
            if (tolower(s[left])!=tolower(s[right]))
                return false;
            left++;
            right--;
        }
        return true;
    }
};
//C#
// public class Solution {
//     public bool IsPalindrome(string s) {
//         StringBuilder sb = new StringBuilder();
        
//         foreach(Char c in s.ToCharArray())
//         {
//             if(char.IsLetterOrDigit(c) )
//             {
//                 sb.Append(c);
//             }
//         }
        
//         String str = sb.ToString().ToLower();
        
//         for(int i = 0; i < str.Length/2; i++)
//         {
//             if(str[str.Length-1-i] !=  str[i])
//                 return false;
//         }
        
//         return true;
//     }
// }

using System.Text.RegularExpressions;

public class Solution {
    public bool IsPalindrome(string s) {

        s = Regex.Replace( s, "[^a-zA-Z0-9]+", "", RegexOptions.Compiled ).ToLower();

        for(int i = 0; i < s.Length/2; i++)
        {
            if(s[s.Length-1-i] !=  s[i])
                return false;
        }
        
        return true;
    }
}
//Java
class Palindrome{
    public static void main(String[] args) {
        System.out.println(new Solution().isPalindrome("A man, a plan, a canal: Panama"));
        System.out.println(new Solution1().isPalindrome("A man, a plan, a canal: Panama"));
    }
}
class Solution {
    public boolean isPalindrome(String s) {
        StringBuilder sb = new StringBuilder();
        
        for(char c : s.toCharArray())
        {
            if(Character.isLetter(c) || Character.isDigit(c) )
            {
                sb.append(c);
            }
        }
        
        String str = sb.toString().toLowerCase();
        
        for(int i = 0; i < str.length()/2; i++)
        {
            if(str.charAt(str.length()-1-i) !=  str.charAt(i))
                return false;
        }
        
        return true;
    }
}

class Solution1{
    public boolean isPalindrome(String s) {

                
        s = s.replaceAll("[^a-zA-Z0-9]","").toLowerCase();
        
        for(int i = 0; i < s.length()/2; i++)
        {
            if(s.charAt(s.length()-1-i) !=  s.charAt(i))
                return false;
        }
        
        return true;
    }
}
//Javascript
var isPalindrome = function(s) {
    s = s.replace(/[^a-zA-Z0-9]/g,'')
    s = s.toLowerCase()
    
    return s == s.split('').reverse().join('')
};

console.log(isPalindrome("A man, a plan, a canal: Panama"));
//Ruby
def is_palindrome(s)
    s.downcase.gsub(/[^a-z\d]/,"") == s.downcase.gsub(/[^a-z\d]/,"").reverse 
end

puts is_palindrome("A man, a plan, a canal: Panama");