Recursive Tower of Hanoi using 4 pegs / rods

Tower of Hanoi is a mathematical puzzle. Traditionally, It consists of three poles and a number of disks of different sizes which can slide onto any poles. The puzzle starts with the disk in a neat stack in ascending order of size in one pole, the smallest at the top thus making a conical shape. The objective of the puzzle is to move all the disks from one pole (say ‘source pole’) to another pole (say ‘destination pole’) with the help of third pole (say auxiliary pole). The puzzle has the following two rules: 1. You can’t place a larger disk onto smaller disk 2. Only one disk can be moved at a time We’ve already discussed recursive solution for Tower of Hanoi with time complexity O(2^n). Using 4 rods, same approach shows significant decrease in time complexity.

Examples:

Input : 3
Output :
Move disk 1 from rod A to rod B
Move disk 2 from rod A to rod C
Move disk 3 from rod A to rod D
Move disk 2 from rod C to rod D
Move disk 1 from rod B to rod D

Input : 5
Output : 
Move disk 1 from rod A to rod C
Move disk 2 from rod A to rod D
Move disk 3 from rod A to rod B
Move disk 2 from rod D to rod B
Move disk 1 from rod C to rod B
Move disk 4 from rod A to rod C
Move disk 5 from rod A to rod D
Move disk 4 from rod C to rod D
Move disk 1 from rod B to rod A
Move disk 2 from rod B to rod C
Move disk 3 from rod B to rod D
Move disk 2 from rod C to rod D
Move disk 1 from rod A to rod D

 Move disk1 from rod A to rod D
 Move disk2 from rod A to rod B
 Move disk1 from rod D to rod B
 Move disk3 from rod A to rod C
 Move disk4 from rod A to rod D
 Move disk3 from rod C to rod D
 Move disk1 from rod B to rod C
 Move disk2 from rod B to rod D
 Move disk1 from rod C to rod D

Time Complexity: O(2^(N/2))
Auxiliary Space: O(1)

This article contributed by madHEYsia.