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71 lines
2.1 KiB
Python
Executable File
71 lines
2.1 KiB
Python
Executable File
#!/usr/bin/env python
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# Sebastian Raschka 2014
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# Functions to calculate factorial, combinations, and permutations
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# bundled in an simple command line interface.
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def factorial(n):
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if n == 0:
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return 1
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else:
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return n * factorial(n-1)
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def combinations(n, r):
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numerator = factorial(n)
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denominator = factorial(r) * factorial(n-r)
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return int(numerator/denominator)
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def permutations(n, r):
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numerator = factorial(n)
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denominator = factorial(n-r)
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return int(numerator/denominator)
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assert(factorial(3) == 6)
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assert(combinations(20, 8) == 125970)
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assert(permutations(30, 3) == 24360)
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if __name__ == '__main__':
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import argparse
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parser = argparse.ArgumentParser(
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description='Script to calculate the number of combinations or permutations ("n choose r")',
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formatter_class=argparse.RawTextHelpFormatter,
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prog='Combinations',
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epilog='Example: ./combinations.py -c 20 3'
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)
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parser.add_argument('-c', '--combinations', type=int, metavar='NUMBER', nargs=2,
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help='Combinations: Number of ways to combine n items with sequence length r where the item order does not matter.')
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parser.add_argument('-p', '--permutations', type=int, metavar='NUMBER', nargs=2,
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help='Permutations: Number of ways to combine n items with sequence length r where the item order does not matter.')
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parser.add_argument('-f', '--factorial', type=int, metavar='NUMBER', help='n! e.g., 5! = 5*4*3*2*1 = 120.')
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parser.add_argument('--version', action='version', version='%(prog)s 1.0')
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args = parser.parse_args()
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if not any((args.combinations, args.permutations, args.factorial)):
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parser.print_help()
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quit()
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if args.factorial:
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print(factorial(args.factorial))
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if args.combinations:
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print(combinations(args.combinations[0], args.combinations[1]))
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if args.permutations:
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print(permutations(args.permutations[0], args.permutations[1]))
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if args.factorial:
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print(factorial(args.factorial))
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