Lecture Notes on 01 August 2011

# recursive solution to Towers of Hanoi
def towers (n, source, spare, dest):
  if (n == 1):
    print "Move disk from ", source, "to", dest
  else:
    towers (n - 1, source, dest, spare)
    print "Move disk from ", source, "to", dest
    towers (n - 1, spare, source, dest)

# gives all subsets or combinations of a given list
def combine (a, b, idxA):
  if (idxA == len(a)):
    print b
    return
  else:
    c = b[:]
    b.append (a[idxA])
    idxA = idxA + 1
    combine (a, b, idxA)
    combine (a, c, idxA)

# gives all permutation of a given list
def permute (a, lo, hi):
  if (lo == hi):
    print a
  else:
    for i in range (lo, hi):
      a[i], a[lo] = a[lo], a[i]
      permute (a, lo + 1, hi)
      a[i], a[lo] = a[lo], a[i]

def main():
  # test towers of hanoi
  n = input ("Enter number of disks: ")
  towers (n, 'A', 'B', 'C')

  # test permutation
  a = ['A', 'B', 'C']
  permute (a, 0, len(a))

  # test combination
  b = []
  combine (a, b, 0)

main()