diff --git a/sorting_searching/selection_sort/selection_sort_challenge.ipynb b/sorting_searching/selection_sort/selection_sort_challenge.ipynb
index 552f470..f45e498 100644
--- a/sorting_searching/selection_sort/selection_sort_challenge.ipynb
+++ b/sorting_searching/selection_sort/selection_sort_challenge.ipynb
@@ -117,6 +117,11 @@
     "class TestSelectionSort(object):\n",
     "\n",
     "    def test_selection_sort(self, func):\n",
+    "        print('None input')\n",
+    "        data = None\n",
+    "        func(data)\n",
+    "        assert_equal(data, None)\n",
+    "\n",
     "        print('Empty input')\n",
     "        data = []\n",
     "        func(data)\n",
@@ -139,7 +144,8 @@
     "    test = TestSelectionSort()\n",
     "    test.test_selection_sort(selection_sort)\n",
     "    try:\n",
-    "        test.test_selection_sort(selection_sort_iterative)\n",
+    "        test.test_selection_sort(selection_sort_recursive)\n",
+    "        test.test_selection_sort(selection_sort_iterative_alt)\n",
     "    except NameError:\n",
     "        # Alternate solutions are only defined\n",
     "        # in the solutions file\n",
@@ -162,21 +168,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.4.3"
   }
  },
  "nbformat": 4,
diff --git a/sorting_searching/selection_sort/selection_sort_solution.ipynb b/sorting_searching/selection_sort/selection_sort_solution.ipynb
index 2f0a9c2..17581a4 100644
--- a/sorting_searching/selection_sort/selection_sort_solution.ipynb
+++ b/sorting_searching/selection_sort/selection_sort_solution.ipynb
@@ -43,7 +43,8 @@
    "source": [
     "## Test Cases\n",
     "\n",
-    "* Empty input -> []\n",
+    "* None -> None\n",
+    "* [] -> []\n",
     "* One element -> [element]\n",
     "* Two or more elements"
    ]
@@ -65,7 +66,8 @@
     "\n",
     "Complexity:\n",
     "* Time: O(n^2) average, worst, best\n",
-    "* Space: O(1) iterative, O(n) recursive (unless tail-call elimination is available, then O(1)), generally not stable"
+    "* Space: O(1) iterative, O(n) recursive (unless tail-call elimination is available, then O(1)), generally not stable\n",
+    "    * Note: Tail call elimination is not inherently available in Python. See the following [StackOverflow post](http://stackoverflow.com/a/13592002)."
    ]
   },
   {
@@ -82,6 +84,35 @@
     "collapsed": true
    },
    "outputs": [],
+   "source": [
+    "def selection_sort(data):\n",
+    "    if data is None:\n",
+    "        return\n",
+    "    size = len(data)\n",
+    "    for i in range(size):\n",
+    "        if i == size - 1:\n",
+    "            break\n",
+    "        min_index = i\n",
+    "        for j in range(i + 1, size):\n",
+    "            if data[j] < data[min_index]:\n",
+    "                min_index = j\n",
+    "        data[i], data[min_index] = data[min_index], data[i]"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "Below are alternate solutions with helper functions:"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": 2,
+   "metadata": {
+    "collapsed": true
+   },
+   "outputs": [],
    "source": [
     "def find_min_index(data, start):\n",
     "    min_index = start\n",
@@ -93,32 +124,20 @@
     "\n",
     "def swap(data, i, j):\n",
     "    if (i != j):\n",
-    "        data[i], data[j] = data[j], data[i]"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 2,
-   "metadata": {
-    "collapsed": false
-   },
-   "outputs": [],
-   "source": [
-    "def selection_sort(data, start=0):\n",
+    "        data[i], data[j] = data[j], data[i]\n",
+    "\n",
+    "\n",
+    "def selection_sort_recursive(data, start=0):\n",
+    "    if data is None:\n",
+    "        return None\n",
     "    if start < len(data) - 1:\n",
     "        swap(data, start, find_min_index(data, start))\n",
-    "        selection_sort(data, start+1)"
-   ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": 3,
-   "metadata": {
-    "collapsed": false
-   },
-   "outputs": [],
-   "source": [
-    "def selection_sort_iterative(data):\n",
+    "        selection_sort_recursive(data, start+1)\n",
+    "\n",
+    "\n",
+    "def selection_sort_iterative_alt(data):\n",
+    "    if data is None:\n",
+    "        return None\n",
     "    if len(data) == 0 or len(data) == 1:\n",
     "        return\n",
     "    for i in range(0, len(data) - 1):\n",
@@ -135,7 +154,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": 3,
    "metadata": {
     "collapsed": false
    },
@@ -156,6 +175,11 @@
     "class TestSelectionSort(object):\n",
     "\n",
     "    def test_selection_sort(self, func):\n",
+    "        print('None input')\n",
+    "        data = None\n",
+    "        func(data)\n",
+    "        assert_equal(data, None)\n",
+    "\n",
     "        print('Empty input')\n",
     "        data = []\n",
     "        func(data)\n",
@@ -178,7 +202,8 @@
     "    test = TestSelectionSort()\n",
     "    test.test_selection_sort(selection_sort)\n",
     "    try:\n",
-    "        test.test_selection_sort(selection_sort_iterative)\n",
+    "        test.test_selection_sort(selection_sort_recursive)\n",
+    "        test.test_selection_sort(selection_sort_iterative_alt)\n",
     "    except NameError:\n",
     "        # Alternate solutions are only defined\n",
     "        # in the solutions file\n",
@@ -191,7 +216,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": 4,
    "metadata": {
     "collapsed": false
    },
@@ -200,11 +225,19 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
+      "None input\n",
       "Empty input\n",
       "One element\n",
       "Two or more elements\n",
       "Success: test_selection_sort\n",
       "\n",
+      "None input\n",
+      "Empty input\n",
+      "One element\n",
+      "Two or more elements\n",
+      "Success: test_selection_sort\n",
+      "\n",
+      "None input\n",
       "Empty input\n",
       "One element\n",
       "Two or more elements\n",
@@ -220,21 +253,21 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 2",
+   "display_name": "Python 3",
    "language": "python",
-   "name": "python2"
+   "name": "python3"
   },
   "language_info": {
    "codemirror_mode": {
     "name": "ipython",
-    "version": 2
+    "version": 3
    },
    "file_extension": ".py",
    "mimetype": "text/x-python",
    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.4.3"
   }
  },
  "nbformat": 4,
diff --git a/sorting_searching/selection_sort/test_selection_sort.py b/sorting_searching/selection_sort/test_selection_sort.py
index 4b59e59..8f5fe03 100644
--- a/sorting_searching/selection_sort/test_selection_sort.py
+++ b/sorting_searching/selection_sort/test_selection_sort.py
@@ -4,6 +4,11 @@ from nose.tools import assert_equal
 class TestSelectionSort(object):
 
     def test_selection_sort(self, func):
+        print('None input')
+        data = None
+        func(data)
+        assert_equal(data, None)
+
         print('Empty input')
         data = []
         func(data)
@@ -26,7 +31,8 @@ def main():
     test = TestSelectionSort()
     test.test_selection_sort(selection_sort)
     try:
-        test.test_selection_sort(selection_sort_iterative)
+        test.test_selection_sort(selection_sort_recursive)
+        test.test_selection_sort(selection_sort_iterative_alt)
     except NameError:
         # Alternate solutions are only defined
         # in the solutions file