Reworked notebook: Added more detail to constraints and test cases. Reworked algorithm discussion and unit test.

stacks-queues/hanoi.ipynb

@@ -13,19 +13,23 @@
    "source": [
     "## Problem: Implement the [Towers of Hanoi](http://en.wikipedia.org/wiki/Tower_of_Hanoi) with 3 towers and N disks.\n",
     "\n",
-    "* [Clarifying Questions](#Clarifying-Questions)\n",
+    "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
     "* [Test Cases](#Test-Cases)\n",
     "* [Algorithm](#Algorithm)\n",
-    "* [Code](#Code)"
+    "* [Code](#Code)\n",
+    "* [Unit Test](#Unit-Test)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Clarifying Questions\n",
+    "## Constraints and Assumptions\n",
     "\n",
-    "* None"
+    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Can we assume we already have a stack class that can be used for this problem?\n",
+    "    * Yes"
    ]
   },
   {
@@ -54,7 +58,7 @@
     "    * hanoi(n-1, buffer, dest)    \n",
     "\n",
     "Complexity:\n",
-    "* Time: O(2^n - 1)\n",
+    "* Time: O(2^n)\n",
     "* Space: O(m) where m is the number of recursion levels"
    ]
   },
@@ -67,7 +71,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 1,
    "metadata": {
     "collapsed": true
    },
@@ -78,7 +82,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 2,
    "metadata": {
     "collapsed": false
    },
@@ -94,32 +98,68 @@
     "        hanoi(num_disks-1, buff, dest, src)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test\n",
+    "\n",
+    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*"
+   ]
+  },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 3,
    "metadata": {
     "collapsed": false
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Test: NULL towers\n",
+      "Test: 0 disks\n",
+      "Test: 1 disk\n",
+      "Test: 2 or more disks\n",
+      "Success: test_hanoi\n"
+     ]
+    }
+   ],
    "source": [
-    "print('NULL towers')\n",
-    "hanoi(num_disks, None, None, None)\n",
-    "first = Stack()\n",
-    "second = Stack()\n",
-    "third = Stack()\n",
-    "print('0 disks')\n",
-    "hanoi(num_disks, first, third, second)\n",
-    "print('1 disk')\n",
-    "first.push(5)\n",
-    "hanoi(num_disks, first, third, second)\n",
-    "print(third.pop())\n",
-    "print('2 or more disks')\n",
-    "num_disks = 3\n",
-    "for i in xrange(num_disks, -1, -1):\n",
-    "    first.push(i)\n",
-    "hanoi(num_disks, first, third, second)\n",
-    "for i in xrange(0, num_disks):\n",
-    "    print(third.pop())"
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class Test(object):\n",
+    "    def test_hanoi(self):\n",
+    "        num_disks = 3\n",
+    "        src = Stack()\n",
+    "        buff = Stack()\n",
+    "        dest = Stack()\n",
+    "\n",
+    "        print('Test: NULL towers')\n",
+    "        hanoi(num_disks, None, None, None)\n",
+    "\n",
+    "        print('Test: 0 disks')\n",
+    "        hanoi(num_disks, src, dest, buff)\n",
+    "        assert_equal(dest.pop(), None)\n",
+    "\n",
+    "        print('Test: 1 disk')\n",
+    "        src.push(5)\n",
+    "        hanoi(num_disks, src, dest, buff)\n",
+    "        assert_equal(dest.pop(), 5)\n",
+    "\n",
+    "        print('Test: 2 or more disks')\n",
+    "        for i in xrange(num_disks, -1, -1):\n",
+    "            src.push(i)\n",
+    "        hanoi(num_disks, src, dest, buff)\n",
+    "        for i in xrange(0, num_disks):\n",
+    "            assert_equal(dest.pop(), i)\n",
+    "\n",
+    "        print('Success: test_hanoi')\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    test = Test()\n",
+    "    test.test_hanoi()"
    ]
   }
  ],