第五题答案:
import java.util.HashMap;
public class MyhashSet<E> {
private HashMap<E,Object> map;
private static final Object PRESENT = new Object();
public MyhashSet() {
map = new HashMap<>();
}
public int size() {
return map.size();
}
public void add(E e) {
map.put(e, PRESENT);
}
public void remove(E e) {
map.remove(e);
}
}