How to create trigger using apex class to count the no of contacts?

Using Apex classes------------------

public class mytriggercount{
public static void counttrigger(contact [] cts){
set<id> accidlist = new set<id>();
for(contact con:cts){
accidlist.add(con.Accountid);
}
list<account> acc = new list<account>();
for(Account a:[select id,my_contacts__c,(select id from contacts)from Account where id IN:accidlist]){
a.my_contacts__c = a.contacts.size();
acc.add(a);
}
update acc;
}
}

trigger-------------------------------

trigger countcontacts1 on Contact (after insert,after update,after delete,after undelete) {
if(trigger.isafter){
if(trigger.isinsert){
mytriggercount.counttrigger(trigger.new);
}
}
if(trigger.isafter){
if(trigger.isundelete){
mytriggercount.counttrigger(trigger.new);
}

}
if(trigger.isafter){
if(trigger.isupdate){
mytriggercount.counttrigger(trigger.new);
}
}
if(trigger.isafter){
if(trigger.isupdate){
mytriggercount.counttrigger(trigger.old);
}
}
if(trigger.isafter){
if(trigger.isdelete){
mytriggercount.counttrigger(trigger.old);
}
}
}