## Sunday, October 8, 2017

### Adventures in Python: Combinations and Permutations

Adventures in Python: Combinations and Permutations

This program offers the user a choice of one of three calculations:

1.  Combinations, no repeats
2.  Permutations
3.  Combinations, with repeats

The program demonstrates how a menu is made.  Equality is tested with two equal signs (==).  A single equal sign (=) represents assignment for the Python.

The math.factorial function uses integers.

#  Program 005: Combinations, Permutations, Repeated Combination
#  Demonstration of the If structure

import math
# factorial is only for integers

# choices
# we will need to format the choice variable as an integer (number)
print("1.  Combination")
print("2.  Permutation")
print("3.  Repeated Combination")
choice = int(input("Choice: "))

# error condition, also input routine
if choice < 1 or choice > 3:
print("Not a valid choice")
else:
n = int(input("n = "))
r = int(input("r = "))
nf = math.factorial(n)
rf = math.factorial(r)
df = math.factorial(n-r)

# calculation test.  Equality is tested using 2 equal signs
if choice == 1:
calc = nf/(df*rf)
print("Combinations = ",calc)

if choice == 2:
calc = nf/df
print("Permutations = ",calc)

if choice == 3:
calc = math.factorial(n+r-1)/(rf*math.factorial(n-1))
print("Combinations = ",calc)

Example: n = 52, r = 5

1.  Combination
2.  Permutation
3.  Repeated Combination
Choice: 1
n = 52
r = 5
Combinations =  2598960.0
>>>
1.  Combination
2.  Permutation
3.  Repeated Combination
Choice: 2
n = 52
r = 5
Permutations =  311875200.0
>>>
1.  Combination
2.  Permutation
3.  Repeated Combination
Choice: 3
n = 52
r = 5
Combinations =  3819816.0

Eddie

This blog is property of Edward Shore, 2017.