# Solves the Tower of Hanoi problem
#
# Matt Bishop, MHI 289I, Fall 2019
# read in a number
# parameters: none
# returns: the number, if read successfully
# 0, on EOF
def getnum():
# loop until we get good input
while True:
try:
# get the input and check the type here
n = int(input("number of disks (EOF to quit): "))
except EOFError: # user wants to quit, so help her
n = 0
break
except ValueError: # user didn't enter a number
print("You have to enter a positive n or EOF")
continue
# now check the value we read/were given
if n > 0:
break
# this is bad, so say so
print("You have to enter a positive n or EOF")
# it's positve to continue, -1 to quit
return n
# solve the Tower of Hanoi
# parameters: n, number of disks to move from fromtower to totower
# fromtower, the name of the tower with the disks
# totower, the name of the tower where the disks are to
# be moved to
# temptower, the name of the tower to be used to hold disks
# temporarily
# returns: nothing
def hanoi(n, fromtower, totower, temptower):
# base case: only one disk, so move it directly to totower
if n == 1:
print("Move disk from tower", fromtower, "to tower", totower)
# recursion here
else:
# move the top n-1 disks to the temporary tower
hanoi(n-1, fromtower, temptower, totower)
# move the leftover disk to the destination
# note: for efficiency, we could just put a copy of the
# base case here
hanoi(1, fromtower, totower, temptower)
# move the n-1 disks from the temporary tower to the destination
hanoi(n-1, temptower, totower, fromtower)
# this puts it all together
def main():
# print out a description of the program
print("""
The Tower of Hanoi puzzle solver will move disks from tower A to tower C.
Tower B is in the middle and is used as a temporary tower.
""")
# get a positive integer
n = getnum()
# got it!
if n > 0:
# solve the problem
hanoi(n, "A", "C", "B")
main()