import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Arrays;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.function.ObjIntConsumer;
import javax.annotation.CheckForNull;

/**
 * Multiset implementation specialized for enum elements, supporting all single-element operations
 * in O(1).
 *