/**
 * A table with forks.  At any time, at most all but one seat can be taken.
 * 
 * @author Franck van Breugel
 */
public class Table {
	private int size;
	private boolean[] pickedUp;
	private int empty; // number of seats that are empty

	/**
	 * Initializes this empty table.
	 * 
	 * @param size the size of this table.
	 */
	public Table(int size) {
		this.size = size;
		this.empty = size;
		this.pickedUp = new boolean[size]; // all false
	}

	/**
	 * Sit down at this table.
	 */
	public synchronized void sitDown() {
		while (this.empty <= 1) {
			try {
				this.wait();
			} catch (InterruptedException e) {}
		}
		// sits down
		this.empty--;
	}
	
	/**
	 * Stand up from this table.
	 */
	public synchronized void standUp() {
		this.empty++;
		this.notifyAll();
	}

	/**
	 * Pick up the fork from this table with the given id.
	 * 
	 * @param id id of the fork.
	 */
	public synchronized void pickUp(int id) {

		while (this.pickedUp[id % this.size]) {
			try {
				this.wait();
			} catch (InterruptedException e) {}
		}
		this.pickedUp[id % this.size] = true;
	}

	/**
	 * Put down the fork on the table with the given id.
	 * 
	 * @param id id of the fork.
	 */
	public synchronized void putDown(int id) {
		this.pickedUp[id % this.size] = false;
		this.notifyAll();
	}
}