This notebook was prepared by Donne Martin. Source and license info is on GitHub.

Challenge Notebook

Problem: Given an array of (unix_timestamp, num_people, EventType.ENTER or EventType.EXIT), find the busiest period.


  • Can we assume the input array is valid?
    • Check for None
  • Can we assume the elements of the input array are valid?
    • Yes
  • Is the input sorted by time?
    • No
  • Can you have enter and exit elements for the same timestamp?
    • Yes you can, order of enter and exit is not guaranteed
  • Could we have multiple enter events (or multiple exit events) for the same timestamp?
    • No
  • What is the format of the output?
    • An array of timestamps [t1, t2]
  • Can we assume the starting number of people is zero?
    • Yes
  • Can we assume the inputs are valid?
    • No
  • Can we assume this fits memory?
    • Yes

Test Cases

  • None -> TypeError
  • [] -> None
  • General case
timestamp  num_people  event_type
1          2           EventType.ENTER
3          1           EventType.ENTER
3          2           EventType.EXIT
7          3           EventType.ENTER
8          2           EventType.EXIT
9          2           EventType.EXIT

result = Period(7, 8)


Refer to the Solution Notebook. If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start.


In [ ]:
from enum import Enum

class Data(object):

    def __init__(self, timestamp, num_people, event_type):
        self.timestamp = timestamp
        self.num_people = num_people
        self.event_type = event_type

    def __lt__(self, other):
        return self.timestamp < other.timestamp

class Period(object):

    def __init__(self, start, end):
        self.start = start
        self.end = end

    def __eq__(self, other):
        return self.start == other.start and self.end == other.end

    def __repr__(self):
        return str(self.start) + ', ' + str(self.end)

class EventType(Enum):

    ENTER = 0
    EXIT = 1
In [ ]:
class Solution(object):

    def find_busiest_period(self, data):
        # TODO: Implement me

Unit Test

The following unit test is expected to fail until you solve the challenge.

In [ ]:
# %load
import unittest

class TestSolution(unittest.TestCase):

    def test_find_busiest_period(self):
        solution = Solution()
        self.assertRaises(TypeError, solution.find_busiest_period, None)
        self.assertEqual(solution.find_busiest_period([]), None)
        data = [
            Data(3, 2, EventType.EXIT),
            Data(1, 2, EventType.ENTER),
            Data(3, 1, EventType.ENTER),
            Data(7, 3, EventType.ENTER),
            Data(9, 2, EventType.EXIT),
            Data(8, 2, EventType.EXIT),
        self.assertEqual(solution.find_busiest_period(data), Period(7, 8))
        print('Success: test_find_busiest_period')

def main():
    test = TestSolution()

if __name__ == '__main__':

Solution Notebook

Review the Solution Notebook for a discussion on algorithms and code solutions.