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class MultiTreeSet<E> {
	TreeMap<E, Integer> freqTreeMap = new TreeMap<E, Integer>();
	int size;
 
	public MultiTreeSet() {}
 
	public MultiTreeSet(Collection<? extends E> c) {
		for(E element : c)
			add(element);
	}
 
	public int size() {
		return size;
	}
 
	public void add(E element) {
		Integer freq = freqTreeMap.get(element);
		if(freq==null)
			freqTreeMap.put(element, 1);
		else
			freqTreeMap.put(element,freq+1);
		++size;
	}
 
	public void remove(E element) {
		Integer freq = freqTreeMap.get(element);
		if(freq!=null) {
			if(freq==1)
				freqTreeMap.remove(element);
			else
				freqTreeMap.put(element, freq-1);
			--size;
		}
	}
 
	public int get(E element) {
		Integer freq = freqTreeMap.get(element);
		if(freq==null)
			return 0;
		return freq;
	}
 
	public boolean contains(E element) {
		return get(element)>0;
	}
 
	public boolean isEmpty() {
		return size==0;
	}
 
	public E first() {
		return freqTreeMap.firstKey();
	}
 
	public E last() {
		return freqTreeMap.lastKey();
	}
 
	public E ceiling(E element) {
		return freqTreeMap.ceilingKey(element);
	}
 
	public E floor(E element) {
		return freqTreeMap.floorKey(element);
	}
 
	public E higher(E element) {
		return freqTreeMap.higherKey(element);
	}
 
	public E lower(E element) {
		return freqTreeMap.lowerKey(element);
	}
}

Main.java:2: error: cannot find symbol
	TreeMap<E, Integer> freqTreeMap = new TreeMap<E, Integer>();
	^
  symbol:   class TreeMap
  location: class MultiTreeSet<E>
  where E is a type-variable:
    E extends Object declared in class MultiTreeSet
Main.java:7: error: cannot find symbol
	public MultiTreeSet(Collection<? extends E> c) {
	                    ^
  symbol:   class Collection
  location: class MultiTreeSet<E>
  where E is a type-variable:
    E extends Object declared in class MultiTreeSet
Main.java:2: error: cannot find symbol
	TreeMap<E, Integer> freqTreeMap = new TreeMap<E, Integer>();
	                                      ^
  symbol:   class TreeMap
  location: class MultiTreeSet<E>
  where E is a type-variable:
    E extends Object declared in class MultiTreeSet
3 errors

Standard output is empty