Coding interview problem : prints all the subsets of a list of numbers (integers).

all_subsets_of_a_set.py

# This is the kind of software engineering interview algorithm you may have to do at Facebook.
# You must print all the subsets of a given set.
#
# If the input is [1, 2, 3], you will have to print :
#
# 1, 2, 3,
# 1, 2,
# 1, 3,
# 1,
# 2, 3,
# 2,
# 3,
#
# In any order you want.

import sys

def printSubsets(set):
  # Here, we use a formula to determine the number of
  # subsets from the length of the given set.
  #
  # We use binary addition and convert this binary value
  # to a list. The '1's of the binary list behaves
  # like a "trigger-key" of the actual set.
  # It will start with : [0, 0, 0]
  # And then : [0, 0, 1] // Prints '3' if the input is [1, 2, 3]
  # And then : [0, 1, 0] // Prints '2' if the input is [1, 2, 3]
  # ...
	max_int = 2 ** len(set)
	for i in reversed(range(0, max_int)):
		bin_list = list("{0:b}".format(i)) 			# Converts decimal to binary string
		for a in range(0, len(set) - len(bin_list)):
			bin_list.insert(0, '0') 			# We have to add trailing '0's
		for n in range(0, len(bin_list)):
			if bin_list[n] == "1":
				sys.stdout.write(str(set[n]) + ", ")	# Avoids carriage return
		sys.stdout.write("\n")

printSubsets([1,2,3])