程序解：現有3L容器和5L容器各一個，問如何量出4L水（水無限）

窮舉所有的可能性，從杯子裏面水變化角度來講，每個狀態到下一個狀態只有6種行爲：3L杯子裝滿，5L杯子裝滿，3L倒空，5L倒空，3L倒到5L，5L倒到3L。最終結果如果5L的裏面有4L水則得到一個解。如果當前狀態和前面一個狀態重複，則取消繼續往後的探索。

public class test{

	private static Status[] steps = new Status[100];

	public static void main(String[] args){
		steps[0] = new Status();
		solve(1);
	}
	
	private static void solve(final int depth){
		//paint(depth-1);
		if(duplicate(depth - 1)){
			return;
		}
		if(steps[depth - 1].cup5 == 4){
			paint(depth - 1);
			return;
		}
		
		Status preStatus = steps[depth - 1];
	
		steps[depth] = preStatus.full3();
		solve(depth + 1);
		
		steps[depth] = preStatus.full5();
		solve(depth + 1);
		
		steps[depth] = preStatus.trans3to5();
		solve(depth + 1);
		
		steps[depth] = preStatus.trans5to3();
		solve(depth + 1);
		
		steps[depth] = preStatus.empty3();
		solve(depth + 1);		
		
		steps[depth] = preStatus.empty5();
		solve(depth + 1);
	}
	
	private static boolean duplicate(int depth){
		for(int i=0 ; i < depth ; i++){
			if( steps[i].equals(steps[depth])){
				return true;
			}
		}
		return false;
	}
	
	private static void paint(int depth){
		for(int i = 0; i <= depth; i++){
			System.out.print(steps[i]+" ");
		}
		System.out.println();
	}
	
}

class Status{
	int cup3;
	int cup5;
	
	public Status(){
	
	}
	
	public Status(Status s){
		this.cup3 = s.cup3;
		this.cup5 = s.cup5;
	}
	
	public Status full3(){
		Status newStatus = new Status(this);
		newStatus.cup3 = 3;
		return newStatus;
	}
	
	public Status full5(){
		Status newStatus = new Status(this);
		newStatus.cup5 = 5;
		return newStatus;
	}
	
	public Status trans3to5(){
		Status newStatus = new Status(this);
		if(5 - newStatus.cup5 >= newStatus.cup3){		
			newStatus.cup5 += newStatus.cup3;
			newStatus.cup3 = 0;
		}else{
			newStatus.cup3 -= (5 - newStatus.cup5);
			newStatus.cup5 = 5;
		}
		return newStatus;		
	}
	
	public Status trans5to3(){
		Status newStatus = new Status(this);
		if(newStatus.cup5 <= 3 - newStatus.cup3){
			newStatus.cup3 += newStatus.cup5;		
			newStatus.cup5 = 0;
		}else{
			newStatus.cup5 -= (3 - newStatus.cup3);
			newStatus.cup3 = 3;
		}
		return newStatus;		
	}
	
	public Status empty3(){
		Status newStatus = new Status(this);
		newStatus.cup3 = 0;
		return newStatus;
	}
	
	public Status empty5(){
		Status newStatus = new Status(this);
		newStatus.cup5 = 0;
		return newStatus;
	}
	
	public String toString(){
		return "["+this.cup3+"#"+this.cup5+"]";
	}
	
	public boolean equals(Object o){
		if(o == null){
			return false;
		}
		if(o == this){
			return true;
		}
		if(o instanceof Status){
			Status s = (Status)o;
			return s.cup3 == this.cup3 && s.cup5 == this.cup5;
		}
		return false;
	}
}