From f7c4ac0d45266ca8c59420038dcc1485d363dffc Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Wed, 29 Mar 2017 04:35:42 -0400
Subject: [PATCH] Add busiest period challenge

---
 online_judges/busiest_period/__init__.py      |   0
 .../busiest_period_challenge.ipynb            | 236 ++++++++++++++
 .../busiest_period_solution.ipynb             | 294 ++++++++++++++++++
 .../test_find_busiest_period.py               |  28 ++
 4 files changed, 558 insertions(+)
 create mode 100644 online_judges/busiest_period/__init__.py
 create mode 100644 online_judges/busiest_period/busiest_period_challenge.ipynb
 create mode 100644 online_judges/busiest_period/busiest_period_solution.ipynb
 create mode 100644 online_judges/busiest_period/test_find_busiest_period.py

diff --git a/online_judges/busiest_period/__init__.py b/online_judges/busiest_period/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/online_judges/busiest_period/busiest_period_challenge.ipynb b/online_judges/busiest_period/busiest_period_challenge.ipynb
new file mode 100644
index 0000000..6a0c77c
--- /dev/null
+++ b/online_judges/busiest_period/busiest_period_challenge.ipynb
@@ -0,0 +1,236 @@
+{
+ "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": [
+    "# Challenge 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)\n",
+    "* [Solution Notebook](#Solution-Notebook)"
+   ]
+  },
+  {
+   "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",
+    "1          2           EventType.ENTER\n",
+    "3          1           EventType.ENTER\n",
+    "3          2           EventType.EXIT\n",
+    "7          3           EventType.ENTER\n",
+    "8          2           EventType.EXIT\n",
+    "9          2           EventType.EXIT\n",
+    "\n",
+    "result = Period(7, 8)\n",
+    "</pre>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "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."
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": true
+   },
+   "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": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "class Solution(object):\n",
+    "\n",
+    "    def find_busiest_period(self, data):\n",
+    "        # TODO: Implement me\n",
+    "        pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "**The following unit test is expected to fail until you solve the challenge.**"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "# %load test_find_busiest_period.py\n",
+    "from nose.tools import assert_equal, assert_raises\n",
+    "\n",
+    "\n",
+    "class TestSolution(object):\n",
+    "\n",
+    "    def test_find_busiest_period(self):\n",
+    "        solution = Solution()\n",
+    "        assert_raises(TypeError, solution.find_busiest_period, None)\n",
+    "        assert_equal(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",
+    "        assert_equal(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": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [Solution Notebook]() for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/online_judges/busiest_period/busiest_period_solution.ipynb b/online_judges/busiest_period/busiest_period_solution.ipynb
new file mode 100644
index 0000000..21fa455
--- /dev/null
+++ b/online_judges/busiest_period/busiest_period_solution.ipynb
@@ -0,0 +1,294 @@
+{
+ "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": {
+    "collapsed": false
+   },
+   "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": {
+    "collapsed": false
+   },
+   "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": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting test_find_busiest_period.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_find_busiest_period.py\n",
+    "from nose.tools import assert_equal, assert_raises\n",
+    "\n",
+    "\n",
+    "class TestSolution(object):\n",
+    "\n",
+    "    def test_find_busiest_period(self):\n",
+    "        solution = Solution()\n",
+    "        assert_raises(TypeError, solution.find_busiest_period, None)\n",
+    "        assert_equal(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",
+    "        assert_equal(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": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_find_busiest_period\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_find_busiest_period.py"
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 3",
+   "language": "python",
+   "name": "python3"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 3
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/online_judges/busiest_period/test_find_busiest_period.py b/online_judges/busiest_period/test_find_busiest_period.py
new file mode 100644
index 0000000..f7c4ed0
--- /dev/null
+++ b/online_judges/busiest_period/test_find_busiest_period.py
@@ -0,0 +1,28 @@
+from nose.tools import assert_equal, assert_raises
+
+
+class TestSolution(object):
+
+    def test_find_busiest_period(self):
+        solution = Solution()
+        assert_raises(TypeError, solution.find_busiest_period, None)
+        assert_equal(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),
+        ]
+        assert_equal(solution.find_busiest_period(data), Period(7, 8))
+        print('Success: test_find_busiest_period')
+
+
+def main():
+    test = TestSolution()
+    test.test_find_busiest_period()
+
+
+if __name__ == '__main__':
+    main()
\ No newline at end of file