riverside.java

传教士与野人过河

import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;

/** 
 * Represents a riverside in the puzzle. 
 */
class RiverSide implements Serializable {
	private ArrayList men = new ArrayList(), boat = new ArrayList();

	public RiverSide(int nMissionary, int nCannibal, boolean withBoat) {
		men.addAll(Collections.nCopies(nMissionary, MACPS.MISSIONARY));
		men.addAll(Collections.nCopies(nCannibal, MACPS.CANNIBAL));
		Collections.sort(men);
		if (withBoat)
			boat.add(MACPS.BOAT);
	}

	public RiverSide deepCopy() {
		return (RiverSide) Copy.deepCopy(this);
	}

	public Collection getMenList() {
		return (Collection) Copy.deepCopy(men);
	}

	public boolean equals(Object otherSide) {
		RiverSide other = (RiverSide) otherSide;
		Collections.sort(men);
		Collections.sort(other.men);
		return this.men.equals(other.men) && this.boat.equals(other.boat);
	}

	public String toString() {
		return "BOAT" + boat + "\t" + "MEN" + men;
	}

	public boolean hasBoat() {
		return !boat.isEmpty();
	}

	// Checks for violation of Rule #1. 
	public boolean fatal() {
		int mCount = 0, cCount = 0;
		for (Iterator i = men.iterator(); i.hasNext();) {
			Object val = i.next();
			if (val.equals(MACPS.MISSIONARY))
				++mCount;
			if (val.equals(MACPS.CANNIBAL))
				++cCount;
		}
		return mCount > 0 && mCount < cCount;
	}

	// Throws SecurityException if the transfer of all men in menList 
	// from this to destination *will* result in violation of Rule #1. 
	// Else, executes the transfer. 
	public void transferMen(RiverSide destination, Collection menList) {
		for (Iterator i = menList.iterator(); i.hasNext();)
			destination.men.add(men.remove(men.indexOf(i.next())));

		// A nice place to automate boat transfer. 
		_transferBoat(destination);

		// Undo the transfer if it led to violation of Rule #1. 
		if (fatal() || destination.fatal()) {
			destination.transferMen(this, menList);
			throw new SecurityException();
		}
	}

	// Tansfers boat from this to destination. Called only by transferMen( ). 
	private void _transferBoat(RiverSide destination) {
		destination.boat.add(boat.remove(0));
	}
}