Lecture Notes on 6 Mar 2017

Read Chapter 4: Recursion

def sum_num (n):
  sum_n = 0
  num = 1
  while (num <= n):
    sum_n += num
    num += 1
  return sum_n

def rec_sum (n):
  if (n == 1):
    return n
  else:
    return n + rec_sum (n - 1)

def rec_sum_list (a, idx):
  if (idx == len(a) - 1):
    return a[idx]
  else:
    return a[idx] + rec_sum_list (a, idx + 1)

def subsets (a, b, lo):
  hi = len(a)
  if (lo == hi):
    print (b)
    return
  else:
    c = b[:]
    b.append (a[lo])
    subsets (a, b, lo + 1)
    subsets (a, c, lo + 1)

def main():
  a = ['A', 'B', 'C', 'D']
  b = []
  subsets (a, b, 0)

main()