Contents.swift

import UIKit

/*
Tower of Hanoi is a mathematical puzzle where we have three rods and n disks. The objective of the puzzle is to move the entire stack to another rod, obeying the following simple rules:
1) Only one disk can be moved at a time.
2) Each move consists of taking the upper disk from one of the stacks and placing it on top of another stack i.e. a disk can only be moved if it is the uppermost disk on a stack.
3) No disk may be placed on top of a smaller disk.



Approach :

Take an example for 2 disks :
Let rod 1 = 'A', rod 2 = 'B', rod 3 = 'C'.

Step 1 : Shift first disk from 'A' to 'B'.
Step 2 : Shift second disk from 'A' to 'C'.
Step 3 : Shift first disk from 'B' to 'C'.

The pattern here is :
Shift 'n-1' disks from 'A' to 'B'.
Shift last disk from 'A' to 'C'.
Shift 'n-1' disks from 'B' to 'C'.

*/

func tower(n: Int, fromRod: String, toRod: String, auxRod: String) {
    if n == 1 {
     print("Move disk 1 from rod " + fromRod + " to rod " + toRod)
    }
    else {
        tower(n: n-1, fromRod: fromRod, toRod: auxRod, auxRod: toRod)
        print("Move disk \(n) fromRod " + fromRod + " to rod " + toRod)
        tower(n: n-1, fromRod: auxRod, toRod: toRod, auxRod: fromRod)
    }
}

tower(n: 4, fromRod: "A", toRod: "C", auxRod: "B")