how to iterate through map in apex code example

Example 1: loop through map apex

for (Id key : Map.keySet()) {
    // The "key" variable is also available inside the loop
    List<String> list = Map.get(key);
    //  logic
}

Example 2: how to iterate map in apex salesforce

for(Id id: mapname.keyset()){
    Set<String> stringset= mapname.get(id);
    for(String a: stringset){
         sendMail(a);
   }