An interview-style programming question.

max_people_living.py

#!/usr/bin/env python3

# Joseph Winters
# January 27, 2017

# Given a list of people with birth years and death years, all of which fall in
# the range [1900, 2000], find the year in which the most people were alive. If
# a person is alive for any part of a year, they count towards the total number
# of living people for that year.


class Person:
    def __init__(self, birth_year, death_year):
        self.birth_year = birth_year
        self.death_year = death_year


def max_population_year(lop, begin_year, end_year):
    years = [0] * (end_year - begin_year + 1)
    for person in lop:
        years[person.birth_year - begin_year] += 1
        if person.death_year != end_year:
            years[person.death_year - begin_year + 1] -= 1
    max_people = 0
    max_year = begin_year
    curr_people = 0
    for index, population_change in enumerate(years):
        curr_people += population_change
        if curr_people > max_people:
            max_people = curr_people
            max_year = begin_year + index
    return max_year


if __name__ == "__main__":
    lop = [
        Person(1945, 1978),
        Person(1940, 1968),
        Person(1911, 1948),
        Person(1925, 1997),
        Person(1901, 1924)
    ]
    print(max_population_year(lop, 1900, 2000))