Rollup Summary using Trigger

//Rollup summary using trigger on conatct
//This is used for  displaying the number of contacts on account

trigger countingcontacsofacc on Contact (after insert,after delete,after update) {
map<id,list<contact>> mapcontactcount=new map<id,list<contact>>();
map<id,Account> accupdate = new map<id,account>();
for(Account acc:[select id,(select id,name from contacts) from account]){
        mapcontactcount.put(acc.id,acc.contacts);
        accupdate .put(acc.id,acc);
}

for(id c:mapcontactcount.keyset()){
    accupdate.get(c).NoofContacts__c=0;
    if(accupdate.get(c)!=null){
        accupdate.get(c).NoofContacts__c=mapcontactcount.get(c).size();
      }
}
     if(accupdate.size()>0)
update accupdate.values();

}