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Towers of Hanoi in Java. This article describes how to solve the Towers of Hanoi in Java.

1. Towers of Hanoi

The towers of hanoi is a popular problem. You have three poles and n disks which fit on the poles. All disks have different sizes. They are stacked on pole 1 in the order of their sizes. The largest disk is on the bottom, the smallest is on the top.

The task is to move all disk from pole 1 to pole 3 under the following restrictions.

  • Only one disk can be moved.

  • A larger disk can not be placed on a smaller disk.

The recursive algorithm works like the following: move n-1 disk from the starting pole to the pole which is neither start nor target (intermediate), move disk n to the target pole and then move n-1 disk from the intermediate pole to the target pole. The n-1 disks are moved recursively.

2. Implementation in Java

Create a Java project "de.vogella.algorithms.towersofhanoi".

Create the following program.

package de.vogella.algorithms.towersofhanoi;

/**
 * Towers of Hanoi
 * Pole are labeled 1, 2,3
 * Each disk is also labeled
 * @author Lars Vogel
 *
 */
public class TowersOfHanoi {
    public static void move(int n, int startPole, int endPole) {
        if (n== 0){
            return;
        }
        int intermediatePole = 6 - startPole - endPole;
        move(n-1, startPole, intermediatePole);
        System.out.println("Move " +n + " from " + startPole + " to " +endPole);
        move(n-1, intermediatePole, endPole);
    }

    public static void main(String[] args) {
        move(5, 1, 3);
    }


}

3. Links and Literature

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4. vogella training and consulting support

Copyright © 2012-2018 vogella GmbH. Free use of the software examples is granted under the terms of the Eclipse Public License 2.0. This tutorial is published under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Germany license.