birthday.py

"""This module contains a code example related to

Think Python, 2nd Edition
by Allen Downey
http://thinkpython2.com

Copyright 2015 Allen Downey

License: http://creativecommons.org/licenses/by/4.0/
"""

from __future__ import print_function, division

import random


def has_duplicates(t):
    """Returns True if any element appears more than once in a sequence.

    t: list

    returns: bool
    """
    # make a copy of t to avoid modifying the parameter
    s = t[:]
    s.sort()

    # check for adjacent elements that are equal
    for i in range(len(s)-1):
        if s[i] == s[i+1]:
            return True
    return False


def random_bdays(n):
    """Returns a list of integers between 1 and 365, with length n.

    n: int

    returns: list of int
    """
    t = []
    for i in range(n):
        bday = random.randint(1, 365)
        t.append(bday)
    return t


def count_matches(num_students, num_simulations):
    """Generates a sample of birthdays and counts duplicates.

    num_students: how many students in the group
    num_samples: how many groups to simulate

    returns: int
    """
    count = 0
    for i in range(num_simulations):
        t = random_bdays(num_students)
        if has_duplicates(t):
            count += 1
    return count


def main():
    """Runs the birthday simulation and prints the number of matches."""
    num_students = 23
    num_simulations = 1000
    count = count_matches(num_students, num_simulations)

    print('After %d simulations' % num_simulations)
    print('with %d students' % num_students)
    print('there were %d simulations with at least one match' % count)


if __name__ == '__main__':
    main()