java - 如果语句在汉诺塔解决方案中无法正常工作

Question

在这段代码中，为了找到汉诺塔问题的解决方案，我将 N(磁盘数量)设置为 4，作为示例，当我运行时，它会打印出以下内容:

import java.util.Scanner;
public class HanoiTower {

  public static void main(String[] args) {
    int N;
    Scanner in=new Scanner(System.in);
    System.out.println("Choose number of disks? ");
    N= in.nextInt();
    in.close();
    towers(N,0,1,2);        
  }

  static void towers(int disks, int a,int b, int spare){ 

    if (disks==1){
      System.out.println("Move disk 1 from 1 to 2 ");
    }
    else{
      towers(disks-1, a,spare,b);
      System.out.printf("Move disk %d from stack %d to stack %d ", disks, a, b);
      towers(disks-1,spare,b,a);
    }
  }
}

我的疑问是为什么它首先打印 if 语句？

 Move disk 1 from 1 to 2 
 Move disk 2 from stack 0 to stack 2 Move disk 1 from 1 to 2 
 Move disk 3 from stack 0 to stack 1 Move disk 1 from 1 to 2 
 Move disk 2 from stack 2 to stack 1 Move disk 1 from 1 to 2 
 Move disk 4 from stack 0 to stack 2 Move disk 1 from 1 to 2 
 Move disk 2 from stack 1 to stack 0 Move disk 1 from 1 to 2 
 Move disk 3 from stack 1 to stack 2 Move disk 1 from 1 to 2 
 Move disk 2 from stack 0 to stack 2 Move disk 1 from 1 to 2 
 Move disk 5 from stack 0 to stack 1 Move disk 1 from 1 to 2 
 Move disk 2 from stack 2 to stack 1 Move disk 1 from 1 to 2 
 Move disk 3 from stack 2 to stack 0 Move disk 1 from 1 to 2 
 Move disk 2 from stack 1 to stack 0 Move disk 1 from 1 to 2 
 Move disk 4 from stack 2 to stack 1 Move disk 1 from 1 to 2 
 Move disk 2 from stack 0 to stack 2 Move disk 1 from 1 to 2 
 Move disk 3 from stack 0 to stack 1 Move disk 1 from 1 to 2 
 Move disk 2 from stack 2 to stack 1 Move disk 1 from 1 to 2 

Answer 1

您的方法towers会递归，直到disks等于1。您可以在开头记录disks的值，例如

static void towers(int disks, int a, int b, int spare) {
    System.out.printf("Disks = %d%n", disks);
    if (disks == 1) {
        System.out.println("Move disk 1 from 1 to 2 ");
    } else {
        towers(disks - 1, a, spare, b);
        System.out.printf("Move disk %d from stack %d to stack %d ", disks,
                a, b);
        towers(disks - 1, spare, b, a);
    }
}

您可以看到为什么会得到这样的输出。另外，关闭 System.in 周围的 Scanner 也是一个坏主意(一旦关闭 System.in，就无法再次打开它)。