mirror of
https://github.com/donnemartin/interactive-coding-challenges.git
synced 2024-03-22 13:11:13 +08:00
295 lines
8.4 KiB
Python
295 lines
8.4 KiB
Python
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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"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)."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Solution Notebook"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Problem: Given an array of (unix_timestamp, num_people, EventType.ENTER or EventType.EXIT), find the busiest period.\n",
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"\n",
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"* [Constraints](#Constraints)\n",
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"* [Test Cases](#Test-Cases)\n",
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"* [Algorithm](#Algorithm)\n",
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"* [Code](#Code)\n",
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"* [Unit Test](#Unit-Test)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Constraints\n",
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"\n",
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"* Can we assume the input array is valid?\n",
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" * Check for None\n",
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"* Can we assume the elements of the input array are valid?\n",
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" * Yes\n",
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"* Is the input sorted by time?\n",
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" * No\n",
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"* Can you have enter and exit elements for the same timestamp?\n",
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" * Yes you can, order of enter and exit is not guaranteed\n",
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"* Could we have multiple enter events (or multiple exit events) for the same timestamp?\n",
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" * No\n",
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"* What is the format of the output?\n",
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" * An array of timestamps [t1, t2]\n",
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"* Can we assume the starting number of people is zero?\n",
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" * Yes\n",
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"* Can we assume the inputs are valid?\n",
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" * No\n",
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"* Can we assume this fits memory?\n",
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" * Yes"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Test Cases\n",
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"\n",
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"* None -> TypeError\n",
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"* [] -> None\n",
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"* General case\n",
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"\n",
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"<pre>\n",
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"timestamp num_people event_type\n",
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"3 2 EventType.EXIT\n",
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"1 2 EventType.ENTER\n",
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"3 1 EventType.ENTER\n",
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"7 3 EventType.ENTER\n",
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"9 2 EventType.EXIT\n",
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"8 2 EventType.EXIT\n",
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"\n",
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"result = Period(7, 8)\n",
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"</pre>"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm\n",
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"\n",
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"Since the input is not sorted, we'll need to sort it first by timestamp, ascending.\n",
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"\n",
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"For each interval in the data set:\n",
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"\n",
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"* If this is an \"enter\" event, increment `curr_people`, else, decrement\n",
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"* Since we can have an \"enter\" and \"exit\" event for the same timestamp, we'll need to look ahead one\n",
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" * If the next element has the same timestamp, hold off (continue) on updating `max_people` and `max_period`\n",
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" * Watch out for indexing out-of-bounds at the end of the array\n",
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"* Update `max_people` and `max_period`\n",
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"\n",
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"Sorted:\n",
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"\n",
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"<pre>\n",
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"timestamp num_people event_type curr_people max_people max_period\n",
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"1 2 EventType.ENTER 2 2 [1, 3]\n",
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"3 1 EventType.ENTER 3 2 (not updated) [1, 3]\n",
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"3 2 EventType.EXIT 1 2 [3, 7]\n",
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"7 3 EventType.ENTER 4 4 [7, 8]\n",
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"8 2 EventType.EXIT 2 4 [7, 8]\n",
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"9 2 EventType.EXIT 0 4 [7, 8]\n",
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"</pre>\n",
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"\n",
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"Complexity:\n",
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"* Time: O(nlog(n)) for the sort\n",
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"* Space: O(1), assuming the sort is in-place"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"from enum import Enum\n",
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"\n",
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"\n",
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"class Data(object):\n",
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"\n",
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" def __init__(self, timestamp, num_people, event_type):\n",
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" self.timestamp = timestamp\n",
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" self.num_people = num_people\n",
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" self.event_type = event_type\n",
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"\n",
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" def __lt__(self, other):\n",
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" return self.timestamp < other.timestamp\n",
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"\n",
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"\n",
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"class Period(object):\n",
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"\n",
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" def __init__(self, start, end):\n",
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" self.start = start\n",
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" self.end = end\n",
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"\n",
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" def __eq__(self, other):\n",
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" return self.start == other.start and self.end == other.end\n",
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"\n",
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" def __repr__(self):\n",
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" return str(self.start) + ', ' + str(self.end)\n",
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"\n",
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"\n",
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"class EventType(Enum):\n",
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"\n",
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" ENTER = 0\n",
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" EXIT = 1"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {
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"collapsed": false
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},
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"outputs": [],
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"source": [
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"class Solution(object):\n",
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"\n",
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" def find_busiest_period(self, data):\n",
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" if data is None:\n",
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" raise TypeError('data cannot be None')\n",
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" if not data:\n",
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" return None\n",
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" data.sort()\n",
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" max_period = Period(0, 0)\n",
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" max_people = 0\n",
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" curr_people = 0\n",
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" for index, interval in enumerate(data):\n",
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" if interval.event_type == EventType.ENTER:\n",
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" curr_people += interval.num_people\n",
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" elif interval.event_type == EventType.EXIT:\n",
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" curr_people -= interval.num_people\n",
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" else:\n",
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" raise ValueError('Invalid event type')\n",
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" if (index < len(data) - 1 and \n",
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" data[index].timestamp == data[index + 1].timestamp):\n",
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" continue\n",
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" if curr_people > max_people:\n",
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" max_people = curr_people\n",
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" max_period.start = data[index].timestamp\n",
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" if index < len(data) - 1:\n",
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" max_period.end = data[index + 1].timestamp\n",
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" else:\n",
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" max_period.end = data[index].timestamp\n",
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" return max_period"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Overwriting test_find_busiest_period.py\n"
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]
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}
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],
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"source": [
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"%%writefile test_find_busiest_period.py\n",
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"from nose.tools import assert_equal, assert_raises\n",
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"\n",
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"\n",
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"class TestSolution(object):\n",
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"\n",
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" def test_find_busiest_period(self):\n",
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" solution = Solution()\n",
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" assert_raises(TypeError, solution.find_busiest_period, None)\n",
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" assert_equal(solution.find_busiest_period([]), None)\n",
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" data = [\n",
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" Data(3, 2, EventType.EXIT),\n",
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" Data(1, 2, EventType.ENTER),\n",
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" Data(3, 1, EventType.ENTER),\n",
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" Data(7, 3, EventType.ENTER),\n",
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" Data(9, 2, EventType.EXIT),\n",
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" Data(8, 2, EventType.EXIT),\n",
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" ]\n",
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" assert_equal(solution.find_busiest_period(data), Period(7, 8))\n",
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" print('Success: test_find_busiest_period')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestSolution()\n",
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" test.test_find_busiest_period()\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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" main()"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {
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"collapsed": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Success: test_find_busiest_period\n"
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]
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}
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],
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"source": [
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"%run -i test_find_busiest_period.py"
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]
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}
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"language": "python",
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"name": "python3"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.0"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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}
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