import java.util.AbstractSet;
import java.util.Iterator;
public class IntSparseSet extends AbstractSet<Integer> {
        private int low, high, n;
    private int[] sparse, dense;
    public IntSparseSet(int low, int high) {
        this.low = low;
        this.high = high;
        n=0;
        sparse = new int[high-low];
        dense = new int[high-low];
    }
    public boolean add(Integer x){
        if(x >= low && x <= high){
                        if (sparse[x-low] >= n || dense[sparse[x-low]] != (x-low)) {
                dense[n] = x-low;
                sparse[x-low] = n;
                n++;
                return true;
                }
        }
        return false;
    }
    public void clear(){
        n = 0;
    }
    public boolean contains(Object x){
            return (((Integer)x>=low) && ((Integer)x < high) && (sparse[(Integer)x-low]<n) && (dense[sparse[(Integer)x-low]] == ((Integer)x-low)));
    }
    public boolean remove(Object x){
        if(contains(x)==true){
            dense[sparse[(Integer) x-low]] = dense[n - 1];
            sparse[dense[n - 1]] = sparse[(Integer) x-low];
            n--;
            return true;
        }
        return false;
    }
    public int size(){
        return n;
    }
    private class MyIterator implements Iterator<Integer>{
        private int i = 0;
                public void remove(){
            IntSparseSet.this.remove(dense[i-1]+low);
        }
        public Integer next(){
            return dense[i++]+low;
        }
        public boolean hasNext(){
            return i < n;
        }
    }
    public Iterator<Integer> iterator(){
        return new MyIterator();
    }
}