interactive-coding-challenges/online_judges/busiest_period/busiest_period_solution.ipynb

287 lines
8.3 KiB
Python

{
"cells": [
{
"cell_type": "markdown",
"metadata": {},
"source": [
"This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Solution Notebook"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Problem: Given an array of (unix_timestamp, num_people, EventType.ENTER or EventType.EXIT), find the busiest period.\n",
"\n",
"* [Constraints](#Constraints)\n",
"* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n",
"* [Code](#Code)\n",
"* [Unit Test](#Unit-Test)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Constraints\n",
"\n",
"* Can we assume the input array is valid?\n",
" * Check for None\n",
"* Can we assume the elements of the input array are valid?\n",
" * Yes\n",
"* Is the input sorted by time?\n",
" * No\n",
"* Can you have enter and exit elements for the same timestamp?\n",
" * Yes you can, order of enter and exit is not guaranteed\n",
"* Could we have multiple enter events (or multiple exit events) for the same timestamp?\n",
" * No\n",
"* What is the format of the output?\n",
" * An array of timestamps [t1, t2]\n",
"* Can we assume the starting number of people is zero?\n",
" * Yes\n",
"* Can we assume the inputs are valid?\n",
" * No\n",
"* Can we assume this fits memory?\n",
" * Yes"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Test Cases\n",
"\n",
"* None -> TypeError\n",
"* [] -> None\n",
"* General case\n",
"\n",
"<pre>\n",
"timestamp num_people event_type\n",
"3 2 EventType.EXIT\n",
"1 2 EventType.ENTER\n",
"3 1 EventType.ENTER\n",
"7 3 EventType.ENTER\n",
"9 2 EventType.EXIT\n",
"8 2 EventType.EXIT\n",
"\n",
"result = Period(7, 8)\n",
"</pre>"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"Since the input is not sorted, we'll need to sort it first by timestamp, ascending.\n",
"\n",
"For each interval in the data set:\n",
"\n",
"* If this is an \"enter\" event, increment `curr_people`, else, decrement\n",
"* Since we can have an \"enter\" and \"exit\" event for the same timestamp, we'll need to look ahead one\n",
" * If the next element has the same timestamp, hold off (continue) on updating `max_people` and `max_period`\n",
" * Watch out for indexing out-of-bounds at the end of the array\n",
"* Update `max_people` and `max_period`\n",
"\n",
"Sorted:\n",
"\n",
"<pre>\n",
"timestamp num_people event_type curr_people max_people max_period\n",
"1 2 EventType.ENTER 2 2 [1, 3]\n",
"3 1 EventType.ENTER 3 2 (not updated) [1, 3]\n",
"3 2 EventType.EXIT 1 2 [3, 7]\n",
"7 3 EventType.ENTER 4 4 [7, 8]\n",
"8 2 EventType.EXIT 2 4 [7, 8]\n",
"9 2 EventType.EXIT 0 4 [7, 8]\n",
"</pre>\n",
"\n",
"Complexity:\n",
"* Time: O(nlog(n)) for the sort\n",
"* Space: O(1), assuming the sort is in-place"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Code"
]
},
{
"cell_type": "code",
"execution_count": 1,
"metadata": {},
"outputs": [],
"source": [
"from enum import Enum\n",
"\n",
"\n",
"class Data(object):\n",
"\n",
" def __init__(self, timestamp, num_people, event_type):\n",
" self.timestamp = timestamp\n",
" self.num_people = num_people\n",
" self.event_type = event_type\n",
"\n",
" def __lt__(self, other):\n",
" return self.timestamp < other.timestamp\n",
"\n",
"\n",
"class Period(object):\n",
"\n",
" def __init__(self, start, end):\n",
" self.start = start\n",
" self.end = end\n",
"\n",
" def __eq__(self, other):\n",
" return self.start == other.start and self.end == other.end\n",
"\n",
" def __repr__(self):\n",
" return str(self.start) + ', ' + str(self.end)\n",
"\n",
"\n",
"class EventType(Enum):\n",
"\n",
" ENTER = 0\n",
" EXIT = 1"
]
},
{
"cell_type": "code",
"execution_count": 2,
"metadata": {},
"outputs": [],
"source": [
"class Solution(object):\n",
"\n",
" def find_busiest_period(self, data):\n",
" if data is None:\n",
" raise TypeError('data cannot be None')\n",
" if not data:\n",
" return None\n",
" data.sort()\n",
" max_period = Period(0, 0)\n",
" max_people = 0\n",
" curr_people = 0\n",
" for index, interval in enumerate(data):\n",
" if interval.event_type == EventType.ENTER:\n",
" curr_people += interval.num_people\n",
" elif interval.event_type == EventType.EXIT:\n",
" curr_people -= interval.num_people\n",
" else:\n",
" raise ValueError('Invalid event type')\n",
" if (index < len(data) - 1 and \n",
" data[index].timestamp == data[index + 1].timestamp):\n",
" continue\n",
" if curr_people > max_people:\n",
" max_people = curr_people\n",
" max_period.start = data[index].timestamp\n",
" if index < len(data) - 1:\n",
" max_period.end = data[index + 1].timestamp\n",
" else:\n",
" max_period.end = data[index].timestamp\n",
" return max_period"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Overwriting test_find_busiest_period.py\n"
]
}
],
"source": [
"%%writefile test_find_busiest_period.py\n",
"import unittest\n",
"\n",
"\n",
"class TestSolution(unittest.TestCase):\n",
"\n",
" def test_find_busiest_period(self):\n",
" solution = Solution()\n",
" self.assertRaises(TypeError, solution.find_busiest_period, None)\n",
" self.assertEqual(solution.find_busiest_period([]), None)\n",
" data = [\n",
" Data(3, 2, EventType.EXIT),\n",
" Data(1, 2, EventType.ENTER),\n",
" Data(3, 1, EventType.ENTER),\n",
" Data(7, 3, EventType.ENTER),\n",
" Data(9, 2, EventType.EXIT),\n",
" Data(8, 2, EventType.EXIT),\n",
" ]\n",
" self.assertEqual(solution.find_busiest_period(data), Period(7, 8))\n",
" print('Success: test_find_busiest_period')\n",
"\n",
"\n",
"def main():\n",
" test = TestSolution()\n",
" test.test_find_busiest_period()\n",
"\n",
"\n",
"if __name__ == '__main__':\n",
" main()"
]
},
{
"cell_type": "code",
"execution_count": 4,
"metadata": {},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Success: test_find_busiest_period\n"
]
}
],
"source": [
"%run -i test_find_busiest_period.py"
]
}
],
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