tower_of_hanoi.py

"""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 = 'SOURCE', rod 2 = 'TEMPORARY', rod 3 = 'DESTINATION'.

Step 1 : Shift first disk from 'SOURCE' to 'TEMPORARY'.
Step 2 : Shift second disk from 'SOURCE' to 'DESTINATION'.
Step 3 : Shift first disk from 'TEMPORARY' to 'DESTINATION'.

The pattern here is :
Shift 'n-1' disks from 'SOURCE' to 'TEMPORARY'.
Shift last disk from 'SOURCE' to 'DESTINATION'.
Shift 'n-1' disks from 'TEMPORARY' to 'DESTINATION'.
"""


def toh(n, s, t, d):
    if n == 1:
        print(s, "-->", d)
        return
    toh(n - 1, s, d, t)
    print(s, "-->", d)
    toh(n - 1, t, s, d)


if __name__ == "__main__":
    while 1:

        n = int(input("""Enter number of disks:"""))

        if n < 0:
            print("Try Again with a valid input")
            continue
        elif n == 0:
            break
        toh(n, "Source", "Temporary", "Destination")

        print("ENTER 0 TO EXIT")