Tower of Hanoi, stop sliding

问题

I developed a solution for the Tower of Hanoi problem:

public static void bewege(int h, char quelle, char ablage, char ziel) {  
  if(h > 0){
     bewege(h - 1, quelle, ziel, ablage);
     System.out.println("Move "+ h +" from " + quelle + " to " + ziel);
     bewege(h - 1, ablage, quelle, ziel);
 }
}

It works fine. Now i want to limit the number of slides and throw an exception if a certain limit is reached. I tried it with a counter but it does not work:

class HanoiNK{

 public static void main(String args[]){
   Integer n = Integer.parseInt(args[0]);
   Integer k = Integer.parseInt(args[1]);

   try{
    bewege(k, n, 'A', 'B', 'C');
   }catch(Exception e){
    System.out.println(e);
   }
 }

 public static void bewege(int c, int h, char quelle, char ablage, char ziel) 
    throws Exception{  
  if(h > 0){
   if(c != 0){
   bewege(c, h - 1, quelle, ziel, ablage);
   c--;
   System.out.println("Move "+ h +" from " + quelle + " to " + ziel);
   bewege(c, h - 1, ablage, quelle, ziel);
   c--;
   }else{ 
    throw new Exception("stop sliding");
   }
  }
 }
}

The exception is never thrown. Any ideas?

UPDATE: result is 6 slides but it should be 5 http://ideone.com/lm084

回答1:

On-topic:

~~It looks to me as though counter is not defined anywhere, and so that shouldn't compile.~~

Now that you've edited your question to fix the above, the exception will be thrown if your first argument is greater than your second argument, e.g.:

java HanoiNK 5 3

The exception will occur when c == 0 and h == 1, in that case.

Off-topic: These lines:

Integer n = Integer.parseInt(args[0]);
Integer k = Integer.parseInt(args[1]);

should be

int n = Integer.parseInt(args[0]);
int k = Integer.parseInt(args[1]);

...since parseInt returns int (not Integer) and the function you're passing them into accepts int (not Integer). Auto-boxing probably lets you get away with it, but it's unnecessary.

回答2:

I think counter == c? Therefore try too move c--; above your bewege(c, h - 1, ablage, quelle, ziel); and it should work, so it looks like this:

 public static void bewege(int c, int h, char quelle, char ablage, char ziel) 
throws Exception{       
    if(h > 0){
        if(c != 0){
        c--;
        bewege(c, h - 1, quelle, ziel, ablage);
        System.out.println("Move "+ h +" from " + quelle + " to " + ziel);
        c--;
        bewege(c, h - 1, ablage, quelle, ziel);
        }else{  
            throw new Exception("stop sliding");
        }
    }
}

回答3:

I'm not sure where the counter variable is declared (doesn't seem to be here), but you're not decrementing it anywhere, so it's value will never change.

来源：https://stackoverflow.com/questions/4570685/tower-of-hanoi-stop-sliding

标签

java

recursion

towers-of-hanoi