Add priority queue challenge

arrays_strings/priority_queue/priority_queue.py

@@ -0,0 +1,41 @@
+import sys
+
+
+class PriorityQueueNode(object):
+
+    def __init__(self, obj, key):
+        self.obj = obj
+        self.key = key
+
+    def __repr__(self):
+        return str(self.obj) + ': ' + str(self.key)
+
+
+class PriorityQueue(object):
+
+    def __init__(self):
+        self.array = []
+
+    def __len__(self):
+        return len(self.array)
+
+    def insert(self, node):
+        self.array.append(node)
+        return self.array[-1]
+
+    def extract_min(self):
+        if not self.array:
+            return None
+        minimum = sys.maxsize
+        for index, node in enumerate(self.array):
+            if node.key < minimum:
+                minimum = node.key
+                minimum_index = index
+        return self.array.pop(minimum_index)
+
+    def decrease_key(self, obj, new_key):
+        for node in self.array:
+            if node.obj is obj:
+                node.key = new_key
+                return node
+        return None

arrays_strings/priority_queue/priority_queue_challenge.ipynb

@@ -0,0 +1,209 @@
+{
+ "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: Implement a priority queue backed by an array.\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",
+    "* Do we expect the methods to be insert, extract_min, and decrease_key?\n",
+    "    * Yes\n",
+    "* Can we assume there aren't any duplicate keys?\n",
+    "    * Yes\n",
+    "* Do we need to validate inputs?\n",
+    "    * No\n",
+    "* Can we assume this fits memory?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "### insert\n",
+    "\n",
+    "* `insert` general case -> inserted node\n",
+    "\n",
+    "### extract_min\n",
+    "\n",
+    "* `extract_min` from an empty list -> None\n",
+    "* `extract_min` general case -> min node\n",
+    "\n",
+    "### decrease_key\n",
+    "\n",
+    "* `decrease_key` an invalid key -> None\n",
+    "* `decrease_key` general case -> updated node"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [Solution Notebook](https://github.com/donnemartin/interactive-coding-challenges/arrays_strings/priority_queue/priority_queue_solution.ipynb).  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": [
+    "class PriorityQueueNode(object):\n",
+    "\n",
+    "    def __init__(self, obj, key):\n",
+    "        self.obj = obj\n",
+    "        self.key = key\n",
+    "\n",
+    "    def __repr__(self):\n",
+    "        return str(self.obj) + ': ' + str(self.key)\n",
+    "\n",
+    "\n",
+    "class PriorityQueue(object):\n",
+    "\n",
+    "    def __init__(self):\n",
+    "        self.array = []\n",
+    "\n",
+    "    def __len__(self):\n",
+    "        return len(self.array)\n",
+    "\n",
+    "    def insert(self, node):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "    def extract_min(self):\n",
+    "        # TODO: Implement me\n",
+    "        pass\n",
+    "\n",
+    "    def decrease_key(self, obj, new_key):\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_priority_queue.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestPriorityQueue(object):\n",
+    "\n",
+    "    def test_priority_queue(self):\n",
+    "        priority_queue = PriorityQueue()\n",
+    "        assert_equal(priority_queue.extract_min(), None)\n",
+    "        priority_queue.insert(PriorityQueueNode('a', 20))\n",
+    "        priority_queue.insert(PriorityQueueNode('b', 5))\n",
+    "        priority_queue.insert(PriorityQueueNode('c', 15))\n",
+    "        priority_queue.insert(PriorityQueueNode('d', 22))\n",
+    "        priority_queue.insert(PriorityQueueNode('e', 40))\n",
+    "        priority_queue.insert(PriorityQueueNode('f', 3))\n",
+    "        priority_queue.decrease_key('f', 2)\n",
+    "        priority_queue.decrease_key('a', 19)\n",
+    "        mins = []\n",
+    "        while priority_queue.array:\n",
+    "            mins.append(priority_queue.extract_min().key)\n",
+    "        assert_equal(mins, [2, 5, 15, 19, 22, 40])\n",
+    "        print('Success: test_min_heap')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestPriorityQueue()\n",
+    "    test.test_priority_queue()\n",
+    "\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [Solution Notebook](https://github.com/donnemartin/interactive-coding-challenges/arrays_strings/priority_queue/priority_queue_solution.ipynb) 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
+}

arrays_strings/priority_queue/priority_queue_solution.ipynb

@@ -0,0 +1,276 @@
+{
+ "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: Implement a priority queue backed by an array.\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",
+    "* Do we expect the methods to be insert, extract_min, and decrease_key?\n",
+    "    * Yes\n",
+    "* Can we assume there aren't any duplicate keys?\n",
+    "    * Yes\n",
+    "* Do we need to validate inputs?\n",
+    "    * No\n",
+    "* Can we assume this fits memory?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "### insert\n",
+    "\n",
+    "* `insert` general case -> inserted node\n",
+    "\n",
+    "### extract_min\n",
+    "\n",
+    "* `extract_min` from an empty list -> None\n",
+    "* `extract_min` general case -> min node\n",
+    "\n",
+    "### decrease_key\n",
+    "\n",
+    "* `decrease_key` an invalid key -> None\n",
+    "* `decrease_key` general case -> updated node"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "### insert\n",
+    "\n",
+    "* Append to the internal array.\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(1)\n",
+    "* Space: O(1)\n",
+    "\n",
+    "### extract_min\n",
+    "\n",
+    "* Loop through each item in the internal array\n",
+    "    * Update the min value as needed\n",
+    "* Remove the min element from the array and return it\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(n)\n",
+    "* Space: O(1)\n",
+    "\n",
+    "### decrease_key\n",
+    "\n",
+    "* Loop through each item in the internal array to find the matching input\n",
+    "    * Update the matching element's key\n",
+    "\n",
+    "Complexity:\n",
+    "* Time: O(n)\n",
+    "* Space: O(1)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 1,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting priority_queue.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile priority_queue.py\n",
+    "import sys\n",
+    "\n",
+    "\n",
+    "class PriorityQueueNode(object):\n",
+    "\n",
+    "    def __init__(self, obj, key):\n",
+    "        self.obj = obj\n",
+    "        self.key = key\n",
+    "\n",
+    "    def __repr__(self):\n",
+    "        return str(self.obj) + ': ' + str(self.key)\n",
+    "\n",
+    "\n",
+    "class PriorityQueue(object):\n",
+    "\n",
+    "    def __init__(self):\n",
+    "        self.array = []\n",
+    "\n",
+    "    def __len__(self):\n",
+    "        return len(self.array)\n",
+    "\n",
+    "    def insert(self, node):\n",
+    "        self.array.append(node)\n",
+    "        return self.array[-1]\n",
+    "\n",
+    "    def extract_min(self):\n",
+    "        if not self.array:\n",
+    "            return None\n",
+    "        minimum = sys.maxsize\n",
+    "        for index, node in enumerate(self.array):\n",
+    "            if node.key < minimum:\n",
+    "                minimum = node.key\n",
+    "                minimum_index = index\n",
+    "        return self.array.pop(minimum_index)\n",
+    "\n",
+    "    def decrease_key(self, obj, new_key):\n",
+    "        for node in self.array:\n",
+    "            if node.obj is obj:\n",
+    "                node.key = new_key\n",
+    "                return node\n",
+    "        return None"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
+   "source": [
+    "%run priority_queue.py"
+   ]
+  },
+  {
+   "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_priority_queue.py\n"
+     ]
+    }
+   ],
+   "source": [
+    "%%writefile test_priority_queue.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestPriorityQueue(object):\n",
+    "\n",
+    "    def test_priority_queue(self):\n",
+    "        priority_queue = PriorityQueue()\n",
+    "        assert_equal(priority_queue.extract_min(), None)\n",
+    "        priority_queue.insert(PriorityQueueNode('a', 20))\n",
+    "        priority_queue.insert(PriorityQueueNode('b', 5))\n",
+    "        priority_queue.insert(PriorityQueueNode('c', 15))\n",
+    "        priority_queue.insert(PriorityQueueNode('d', 22))\n",
+    "        priority_queue.insert(PriorityQueueNode('e', 40))\n",
+    "        priority_queue.insert(PriorityQueueNode('f', 3))\n",
+    "        priority_queue.decrease_key('f', 2)\n",
+    "        priority_queue.decrease_key('a', 19)\n",
+    "        mins = []\n",
+    "        while priority_queue.array:\n",
+    "            mins.append(priority_queue.extract_min().key)\n",
+    "        assert_equal(mins, [2, 5, 15, 19, 22, 40])\n",
+    "        print('Success: test_min_heap')\n",
+    "\n",
+    "\n",
+    "def main():\n",
+    "    test = TestPriorityQueue()\n",
+    "    test.test_priority_queue()\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_min_heap\n"
+     ]
+    }
+   ],
+   "source": [
+    "%run -i test_priority_queue.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
+}

arrays_strings/priority_queue/test_priority_queue.py

@@ -0,0 +1,30 @@
+from nose.tools import assert_equal
+
+
+class TestPriorityQueue(object):
+
+    def test_priority_queue(self):
+        priority_queue = PriorityQueue()
+        assert_equal(priority_queue.extract_min(), None)
+        priority_queue.insert(PriorityQueueNode('a', 20))
+        priority_queue.insert(PriorityQueueNode('b', 5))
+        priority_queue.insert(PriorityQueueNode('c', 15))
+        priority_queue.insert(PriorityQueueNode('d', 22))
+        priority_queue.insert(PriorityQueueNode('e', 40))
+        priority_queue.insert(PriorityQueueNode('f', 3))
+        priority_queue.decrease_key('f', 2)
+        priority_queue.decrease_key('a', 19)
+        mins = []
+        while priority_queue.array:
+            mins.append(priority_queue.extract_min().key)
+        assert_equal(mins, [2, 5, 15, 19, 22, 40])
+        print('Success: test_min_heap')
+
+
+def main():
+    test = TestPriorityQueue()
+    test.test_priority_queue()
+
+
+if __name__ == '__main__':
+    main()