学步园

可以用递归实现，递归算法：

A source tower,B buffer tower ,C destination tower
1. Move the subtree consisting of the top n-1 disks from A to B.
2. Move the remaining (largest) disk from A to C.
3. Move the subtree from B to C.

Base Case：How do you move a subtree of two disks from A to C? Move the subtree consisting of only one disk (1) from A to B. This is the base case: When you’re moving only one disk, you just move it; there’s nothing else to do. Then move the larger disk (2)
from A to C, and replace the subtree (disk 1) on it.

从A移动到C的过程如下：

柱子数据结构：用栈实现

class Tower{
  pirvate Stack diskStack;
  private int index; //the current tower's index in the Towers arrary
  public Tower(i){
    diskStack=new Stack();
	index=i;
  }
  
  public void add(int d){
    if(!diskStack.isEmpty() && diskStack.peek()<=d){
	   System.out.println("Error placing disk " +d);
	}
	else
	   diskStack.push(d);
  }//end add
  
  public int getIndex(){
   return index;
  }//end getIndex()
}//end class Tower

汉诺塔代码

public static void main(String[] args){
   int diskNumber=5; //disks number
   int towerNumber=3; //tower number 
   
   Tower[] towers=new Tower[3];
   //initial tower's index in the towers' array
   for(int i=0;i<3;i++)
     towers[i]=new Tower(i);
   //initial towers[0]
   for(int i=diskNumber-1;i>=0;i--)
     towers[0].add(i);
	 
   //move disk from 0 to 2
   moveDisks(n,towers[0],towers[1],towers[2]);  
}//end main

public static moveDisks(int n,Tower from,Tower buffer,Tower to){
  if(n==1)  //base case
    moveTop(from,to);
  else{
    moveDisks(n-1,from,to,buffer);  //from A to B
	moveTop(from,to);//from A to C
	moveDisks(n-1,buffer,from,to);//from B to C
  }//end else
}//end moveDisks()

private static moveTop(Tower from,Tower to){
   int top=from.pop(); 
   to.add(top);
   System.out.println("Move disk "+top+" from "+ from.getIndex()+" to "+ to.getIndex() );
}//end moveTop()