CC3.4.java

/*3.4 In the classic problem of the Towers of Hanoi, you have 3 towers and Ndisks of different sizes which can slide onto any tower.
The puzzle starts with disks sorted in ascending order of size from top to bottom 
(i.e., each disk sits on top of an even larger one). You have the following constraints:
(1) Only one disk can be moved at a time.
(2) A disk is slid off the top of one tower onto the next tower.
(3) A disk can only be placed on top of a larger disk.
Write a program to move the disks from the first tower to the last using stacks.*/


class Tower {
    private Stack<Integer> disks;
    priate int index;
    public Tower(int i) {
        disks = new Stack<Integer>();
        index = i;
    }
    public int index() {
        return index;
    }
    public void add(int d) {
        if(!disks.isEmpty() && disks.peek()<=d) {
            throw new Exception("Error placing disk"+d);
        } else {
            disks.push(d);
        }
    }
    public void moveTopTo(Tower t) {
        int top = disks.pop();
        t.add(top);
    }
    public void moveDisks(int n, Tower destination, Tower buffer) {
        if(n>0) {
            moveDisks(n-1, buffer, destination);
            moveTopTo(destination);
            buffer.moveDisks(n-1, destination, this);
        }
    }
}

public class Solution {
    public static void main(String[] args) {
        int n=3;
        Tower[] towers = new Tower[n];
        for(int i=0; i<3; i++) {
            towers[i] = new Tower(i);
        }
        for(int i=n-1; i>=0; i--) {
            towers[0].add(i);
        }
        towers[0].moveDisks(n, towers[2], towers[1]);
    }
}