Leetcode Longest Palindrome problem solution

class Solution:
    def longestPalindrome(self, s: str) -> int:
        a = set()
        for l in s:
            if l not in a:
                a.add(l)
            else:
                a.remove(l)
        return len(s) - len(a) + 1 if len(a) else len(s)

public class Solution {
    public int longestPalindrome(String s) {
        if(s==null|| s.length()==0)
        return 0;
        if(s.length()==1)
        return 1;
        
        int[] alpha=new int[128];
        int max_length=0;
        for(char c:s.toCharArray()){
            alpha[c]++;
            if(alpha[c]==2)
            {
                max_length+=2;
                alpha[c]=0;
            }
        }
        if(s.length()>max_length)
         return max_length+1;
        else
         return max_length;
        
    }
}

int longestPalindrome(string s) {
        if (s.size() < 2) return s.size();
        int ht[256]{0};
        for (auto a : s) ++ht[a];
        int length{0};
        bool has_odd{false};
        for (int i = 65; i <= 122; ++i) {
            if (ht[i]) {
                length += ht[i];
                if (ht[i] % 2 == 1) {
                    if (!has_odd) has_odd = true;
                    length -= 1;
                }
            }
        }
        if (has_odd) ++length;
        return length;
    }

#include<string.h>
int longestPalindrome(char * s){
    int count[52]={0};
    int len=strlen(s);
    for(int i=0;i<len;i++){
        if(s[i]<='Z' && s[i]>='A'){
            count[26+s[i]-'A']++;
        }else{
            count[s[i]-'a']++;
        }
    }
    int ans=0;
    bool odd=false;
    for(int i=0;i<52;i++){
        if(count[i]%2){
            ans+=(count[i]-1);
            odd=true;  
        }else{
            ans+=count[i];
        }
    }
    return odd?ans+1:ans;
}