Can anybody correct this code or give me a code which summerize number of contacts on account?

global class scheduledCalculatebookings implements Schedulable {
   global void execute(SchedulableContext sc) {
       /* System.debug('Schedule');
      calculateBooking b = new calculateBooking();
      database.executebatch(b);*/
  
  
  
  
   Map<Id, List<Contact>> AcctContactList = new Map<Id, List<Contact>>();
    Set<Id> AcctIds = new Set<Id>();   
    List<Account> AcctList = new List<Account>();
    List<Account> AcctOld = new List<Account>();
    List<Contact> ConList = new List<Contact>();
    AcctOld = [SELECT Id FROM Account];
   
    for(Account old : AcctOld)
    {
        AcctIds.add(old.Id);
       
    if(AcctIds.size() > 0){
        ConList = [SELECT Id, AccountId FROM Contact WHERE AccountId IN : AcctIds];
       
        for(Contact Con : ConList) {
            if(!AcctContactList.containsKey(Con.AccountId)){
                AcctContactList.put(Con.AccountId, new List<Contact>());
            }
            AcctContactList.get(Con.AccountId).add(Con);     
        }                          
       
        System.debug('Account Id and Contact List Map is ' + AcctContactList);
           
        AcctList = [SELECT Open_Activity_Count_c__c FROM Account WHERE Id IN : AcctIds];
       
        for(Account Acc : AcctList) {
            List<Contact> ContList = new List<Contact>();
            ContList = AcctContactList.get(Acc.Id);
            Acc.Open_Activity_Count_c__c = ContList.size();
        }   
       
        System.debug('Account List is ' + AcctList);
        update AcctList;  
     }

     }
   
  
       
    //Send an email to the User after your batch completes
    Messaging.SingleEmailMessage mail = new Messaging.SingleEmailMessage();
    String[] toAddresses = new String[] {'test@gmail.com'};
    mail.setToAddresses(toAddresses);
    mail.setSubject('Apex Batch Job Calculate Bookings');
    mail.setPlainTextBody('The batch Apex job processed ');
    Messaging.sendEmail(new Messaging.SingleEmailMessage[] { mail });
     }
}