added both solutions w/ test

arrays_strings/group_items/group_ordered_solution.ipynb

@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<small><i>This notebook was prepared by [Author](https://github.com/). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
+    "<small><i>This notebook was prepared by [wdonahoe](https://github.com/wdonahoe). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
    ]
   },
   {
@@ -18,12 +18,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Problem: Implement foo(val), which returns val\n",
+    "## Problem: Implement a function that groups identical items based on their order in the list.\n",
     "\n",
     "* [Constraints](#Constraints)\n",
     "* [Test Cases](#Test-Cases)\n",
-    "* [Algorithm](#Algorithm)\n",
-    "* [Code](#Code)\n",
+    "* [Algorithm: Modified Selection Sort](#Algorithm: Modified Selection Sort)\n",
+    "* [Code: Modified Selection Sort](#Code: Modified Selection Sort)\n",
+    "* [Algorithm: Ordered Dict](#Algorithm: Ordered Dict)\n",
+    "* [Code: Ordered Dict](#Code:-Ordered-Dict)\n",
     "* [Unit Test](#Unit-Test)"
    ]
   },
@@ -33,9 +35,8 @@
    "source": [
     "## Constraints\n",
     "\n",
-
-    "* Is it foo or bar?\n",
-    "    * foo"
+    "* Can we use extra data structures?\n",
+    "    * Yes"
    ]
   },
   {
@@ -44,82 +45,118 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* foo(val) -> val"
+    "* group_ordered([1,2,1,3,2]) -> [1,1,2,2,3]\n",
+    "* group_ordered(['a','b','a') -> ['a','a','b']\n",
+    "* group_ordered([1,1,2,3,4,5,2,1]-> [1,1,1,2,2,3,4,5]\n",
+    "* group_ordered([]) -> []\n",
+    "* group_ordered([1]) -> [1]\n",
+    "* group_ordered(None) -> None\n"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Algorithm\n",
+    "## Algorithm: Modified Selection Sort\n",
     "\n",
-    "Return the input, val\n",
+    "* Save the relative position of the first-occurence of each item in a list.\n",
+    "* Iterate through list of unique items.\n",
+    "    * Keep an outer index; scan rest of list, swapping matching items with outer index and incrementing outer index each time. \n",
     "    \n",
     "Complexity:\n",
-    "* Time: O(1)\n",
-    "* Space: O(1)"
+    "* Time: O(n^2)\n",
+    "* Space: O(n)"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Code"
+    "# Code: Modified Selection Sort"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 5,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "def foo(val):\n",
-    "    return val"
+    "def make_order_list(list_in):\n",
+    "    order_list = []\n",
+    "    for item in list_in:\n",
+    "        if item not in order_list:\n",
+    "            order_list.append(item)\n",
+    "    return order_list\n",
+    "\n",
+    "\n",
+    "def group_ordered(list_in):\n",
+    "    if list_in is None:\n",
+    "        return None\n",
+    "    order_list = make_order_list(list_in)\n",
+    "    current = 0\n",
+    "    for item in order_list:\n",
+    "        search = current + 1\n",
+    "        while True:\n",
+    "            try:\n",
+    "                if list_in[search] != item:\n",
+    "                    search += 1\n",
+    "                else:\n",
+    "                    current += 1\n",
+    "                    list_in[current], list_in[search] = list_in[search], list_in[current]\n",
+    "                    search += 1\n",
+    "            except IndexError:\n",
+    "                break\n",
+    "    return list_in"
    ]
   },
   {
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Unit Test"
+    "## Algorithm: Ordered Dict.\n",
+    "\n",
+    "* Use an ordered dict to track insertion order of each key\n",
+    "* Flatten list of values.\n",
+    "\n",
+    "Complexity:\n",
+    "\n",
+    "* Time: O(n)\n",
+    "* Space: O(n)"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Code: Ordered Dict"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": null,
    "metadata": {
-    "collapsed": false
+    "collapsed": true
    },
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "Overwriting test_foo.py\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
-    "%%writefile test_foo.py\n",
-    "from nose.tools import assert_equal\n",
+    "from collections import OrderedDict\n",
     "\n",
+    "def group_ordered(list_in):\n",
+    "    result = OrderedDict()\n",
+    "    for value in list_in:\n",
+    "        result.setdefault(value, []).append(value)\n",
+    "    return [v for group in result.values() for v in group]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test\n",
     "\n",
-    "class TestFoo(object):\n",
-    "\n",
-    "    def test_foo(self):\n",
-    "        assert_equal(foo(None), None)\n",
-    "        assert_equal(foo(0), 0)\n",
-    "        assert_equal(foo('bar'), 'bar')\n",
-    "        print('Success: test_foo')\n",
-    "\n",
-    "def main():\n",
-    "    test = TestFoo()\n",
-    "    test.test_foo()\n",
-    "\n",
-    "if __name__ == '__main__':\n",
-    "    main()"
+    "#### The following unit test is expected to fail until you solve the challenge."
    ]
   },
   {
@@ -133,16 +170,47 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Success: test_foo\n"
+      "Overwriting test_group_ordered.py\n"
      ]
     }
    ],
    "source": [
-    "%run -i test_foo.py"
+    "%%writefile test_group_ordered.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "class TestGroupOrdered(object):\n",
+    "\n",
+    "    def test_group_ordered(self):\n",
+    "        assert_equal(group_ordered(None), None)\n",
+    "        assert_equal(group_ordered([]), [])\n",
+    "        assert_equal(group_ordered([1]), [1])\n",
+    "        assert_equal(group_ordered([1,2,1,3,2]),[1,1,2,2,3])\n",
+    "        assert_equal(group_ordered(['a','b','a']),['a','a','b'])\n",
+    "        assert_equal(group_ordered([1,1,2,3,4,5,2,1]),[1,1,1,2,2,3,4,5])\n",
+    "        assert_equal(group_ordered([1,2,3,4,3,4]),[1,2,3,3,4,4])\n",
+    "\n",
+    "def main():\n",
+    "    test = TestGroupOrdered()\n",
+    "    test.test_group_ordered()\n",
+    "\n",
+    "if __name__ == '__main__':\n",
+    "    main()\n"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 4,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "%run -i test_group_ordered.py"
    ]
   }
  ],
  "metadata": {
+  "celltoolbar": "Edit Metadata",
   "kernelspec": {
    "display_name": "Python 2",
    "language": "python",
@@ -158,7 +226,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "version": "2.7.6"
   }
  },
  "nbformat": 4,