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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ncr(n, r):
 """ Calculate n choose r. :param n: n :type n : int :param r: r :type r :int :return: n choose r as int """

    r = min(r, n - r)
    numer = reduce(op.mul, range(n, n - r, -1), 1)
    denom = reduce(op.mul, range(1, r + 1), 1)
    return numer // denom