Hướng dẫn dùng combinatorial calculator python

Do you want iteration? itertools.combinations. Common usage:

>>> import itertools
>>> itertools.combinations['abcd',2]

>>> list[itertools.combinations['abcd',2]]
[['a', 'b'], ['a', 'c'], ['a', 'd'], ['b', 'c'], ['b', 'd'], ['c', 'd']]
>>> [''.join[x] for x in itertools.combinations['abcd',2]]
['ab', 'ac', 'ad', 'bc', 'bd', 'cd']

If you just need to compute the formula, math.factorial can be used, but is not fast for large combinations, but see math.comb below for an optimized calculation available in Python 3.8+:

import math

def nCr[n,r]:
    f = math.factorial
    return f[n] // f[r] // f[n-r]

if __name__ == '__main__':
    print nCr[4,2]

Output:

6

As of Python 3.8, math.comb can be used and is much faster:

>>> import math
>>> math.comb[4,2]
6