import java.util.*;

// Stores a set of integers within the given range
public class RangeSet {
    // restriction: cannot use a set
    private int[] data;
    private int size;

    // creates a RangeSet able to store integers from
    // 0(inclusive) to given max (exclusive)
    public RangeSet() {
        data = new boolean[max];
        size = 0;
    }
    
    // pre: num is < max of range for this set, throws IllegalArgumentException if otherwise
    // adds the given number to the set
    public void add(int num) {

        if (!data[num]) {
            data[num] = true;
            size++;
        }
    }
    
    // pre: num is < max of range for this set, throws IllegalArgumentException if otherwise
    // post: removes the given number from the set
    public void remove(int num) {
        checkRange(num);
        if (data[num]) {
            data[num] = false;
            size--;
        }
    }
    
    // pre: num is < max of range for this set, throws IllegalArgumentException if otherwise
    // post: returns true if the given num is in the set, false otherwise
    public boolean contains(int num) {
        checkRange(num);
        return data[num];
    }
    
    // post: returns the number of elements in the set
    public int size() {
        return size;
    }
    
    // throws an IllegalArgumentException if num is >= max of range
    private void checkRange(int num) {
        if (num >= max) {
           throw new IllegalArgumentException("num to add is outside of range");
        }
    }
}