diff --git a/arrays_strings/permutation/permutation_solution.ipynb b/arrays_strings/permutation/permutation_solution.ipynb
index 8f4589c..6eb4e58 100644
--- a/arrays_strings/permutation/permutation_solution.ipynb
+++ b/arrays_strings/permutation/permutation_solution.ipynb
@@ -35,6 +35,7 @@
    "source": [
     "## Constraints\n",
     "\n",
+
     "* Can we assume the string is ASCII?\n",
     "    * Yes\n",
     "    * Note: Unicode strings could require special handling depending on your language\n",
@@ -163,7 +164,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 3,
    "metadata": {
     "collapsed": false
    },
@@ -241,7 +242,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.6"
+   "version": "2.7.10"
   }
  },
  "nbformat": 4,
diff --git a/arrays_strings/rotation/rotation_challenge.ipynb b/arrays_strings/rotation/rotation_challenge.ipynb
index c892cb2..e66ebe3 100644
--- a/arrays_strings/rotation/rotation_challenge.ipynb
+++ b/arrays_strings/rotation/rotation_challenge.ipynb
@@ -34,6 +34,7 @@
    "source": [
     "## Constraints\n",
     "\n",
+
     "* Can you assume the string is ASCII?\n",
     "    * Yes\n",
     "    * Note: Unicode strings could require special handling depending on your language\n",
@@ -74,38 +75,20 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "def is_substring(substr, s):\n",
-    "    if len(s) < len(substr):\n",
-    "        return False\n",
-    "    elif len(substr) == len(s) and len(s) == 0:\n",
-    "        return True\n",
-    "    pos = 0\n",
-    "    while pos < len(s):\n",
-    "        so_far = 0\n",
-    "        while so_far < len(substr):\n",
-    "            if substr[so_far] != s[pos]:\n",
-    "                pos = pos + 1\n",
-    "                break\n",
-    "            else:\n",
-    "                pos = pos + 1\n",
-    "                so_far = so_far + 1\n",
-    "        if so_far == len(substr):\n",
-    "            return True\n",
-    "    return False\n",
+    "def is_substring(s1, s2):\n",
+    "    # TODO: Implement me\n",
+    "    pass\n",
     "\n",
     "def is_rotation(s1, s2):\n",
-    "    if s1 is None or s2 is None:\n",
-    "        return False\n",
-    "    elif len(s1) != len(s2):\n",
-    "        return False\n",
-    "    else:\n",
-    "        return is_substring(s2,s1+s1)"
+    "    # TODO: Implement me\n",
+    "    # Call is_substring only once\n",
+    "    pass"
    ]
   },
   {
@@ -126,19 +109,11 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 6,
+   "execution_count": null,
    "metadata": {
     "collapsed": false
    },
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "Success: test_rotation\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "# %load test_rotation.py\n",
     "from nose.tools import assert_equal\n",
@@ -188,7 +163,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.6"
+   "version": "2.7.10"
   }
  },
  "nbformat": 4,
diff --git a/arrays_strings/unique_chars/unique_chars_challenge.ipynb b/arrays_strings/unique_chars/unique_chars_challenge.ipynb
index c9ffbff..0e85a04 100644
--- a/arrays_strings/unique_chars/unique_chars_challenge.ipynb
+++ b/arrays_strings/unique_chars/unique_chars_challenge.ipynb
@@ -34,6 +34,7 @@
    "source": [
     "## Constraints\n",
     "\n",
+
     "* Can you assume the string is ASCII?\n",
     "    * Yes\n",
     "    * Note: Unicode strings could require special handling depending on your language\n",
@@ -72,22 +73,15 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 2,
+   "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
     "def unique_chars(string):\n",
-    "    from collections import defaultdict\n",
-    "    \n",
-    "    char_table = defaultdict(int)\n",
-    "    for c in string:\n",
-    "        if char_table[c] > 0:\n",
-    "            return False\n",
-    "        else:\n",
-    "            char_table[c] = 1\n",
-    "    return True"
+    "    # TODO: Implement me\n",
+    "    pass"
    ]
   },
   {
@@ -106,19 +100,11 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": null,
    "metadata": {
     "collapsed": false
    },
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "Success: test_unique_chars\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "# %load test_unique_chars.py\n",
     "from nose.tools import assert_equal\n",
@@ -173,7 +159,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.6"
+   "version": "2.7.10"
   }
  },
  "nbformat": 4,
diff --git a/sorting_searching/insertion_sort/insertion_sort_challenge.ipynb b/sorting_searching/insertion_sort/insertion_sort_challenge.ipynb
index b35d575..c8a7f69 100644
--- a/sorting_searching/insertion_sort/insertion_sort_challenge.ipynb
+++ b/sorting_searching/insertion_sort/insertion_sort_challenge.ipynb
@@ -34,6 +34,7 @@
    "source": [
     "## Constraints\n",
     "\n",
+
     "* Is a naiive solution sufficient?\n",
     "    * Yes"
    ]
@@ -67,25 +68,15 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 4,
+   "execution_count": null,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "def insert(l,item_pos):\n",
-    "    item = l[item_pos]\n",
-    "    while item_pos > 0:\n",
-    "        if l[item_pos - 1] > item:\n",
-    "            l[item_pos - 1], l[item_pos] = l[item_pos], l[item_pos - 1]\n",
-    "            item_pos -= 1\n",
-    "        else:\n",
-    "            break\n",
-    "\n",
     "def insertion_sort(data):\n",
-    "    for i,item in enumerate(data):\n",
-    "        insert(data,i)\n",
-    "    return data"
+    "    # TODO: Implement me\n",
+    "    pass"
    ]
   },
   {
@@ -101,22 +92,11 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 5,
+   "execution_count": null,
    "metadata": {
     "collapsed": false
    },
-   "outputs": [
-    {
-     "name": "stdout",
-     "output_type": "stream",
-     "text": [
-      "Empty input\n",
-      "One element\n",
-      "Two or more elements\n",
-      "Success: test_insertion_sort\n"
-     ]
-    }
-   ],
+   "outputs": [],
    "source": [
     "# %load test_insertion_sort.py\n",
     "from nose.tools import assert_equal\n",
@@ -173,7 +153,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.6"
+   "version": "2.7.10"
   }
  },
  "nbformat": 4,
diff --git a/sorting_searching/insertion_sort/insertion_sort_solution.ipynb b/sorting_searching/insertion_sort/insertion_sort_solution.ipynb
index 3d865e9..83314b7 100644
--- a/sorting_searching/insertion_sort/insertion_sort_solution.ipynb
+++ b/sorting_searching/insertion_sort/insertion_sort_solution.ipynb
@@ -33,6 +33,7 @@
    "source": [
     "## Constraints\n",
     "\n",
+
     "* Is a naiive solution sufficient?\n",
     "    * Yes"
    ]
@@ -151,7 +152,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 1,
+   "execution_count": 3,
    "metadata": {
     "collapsed": false
    },
@@ -160,34 +161,16 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Empty input\n"
-     ]
-    },
-    {
-     "ename": "NameError",
-     "evalue": "global name 'insertion_sort' is not defined",
-     "output_type": "error",
-     "traceback": [
-      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
-      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
-      "\u001b[1;32m/home/wdonahoe/Documents/interactive-coding-challenges/sorting_searching/insertion_sort/test_insertion_sort.py\u001b[0m in \u001b[0;36m<module>\u001b[1;34m()\u001b[0m\n\u001b[0;32m     24\u001b[0m \u001b[1;32mif\u001b[0m \u001b[0m__name__\u001b[0m \u001b[1;33m==\u001b[0m \u001b[1;34m'__main__'\u001b[0m\u001b[1;33m:\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     25\u001b[0m     \u001b[0mtest\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mTestInsertionSort\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m---> 26\u001b[1;33m     \u001b[0mtest\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0mtest_insertion_sort\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
-      "\u001b[1;32m/home/wdonahoe/Documents/interactive-coding-challenges/sorting_searching/insertion_sort/test_insertion_sort.py\u001b[0m in \u001b[0;36mtest_insertion_sort\u001b[1;34m(self)\u001b[0m\n\u001b[0;32m      7\u001b[0m         \u001b[1;32mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m'Empty input'\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m      8\u001b[0m         \u001b[0mdata\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;33m[\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 9\u001b[1;33m         \u001b[0minsertion_sort\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mdata\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m     10\u001b[0m         \u001b[0massert_equal\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mdata\u001b[0m\u001b[1;33m,\u001b[0m \u001b[1;33m[\u001b[0m\u001b[1;33m]\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m     11\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n",
-      "\u001b[1;31mNameError\u001b[0m: global name 'insertion_sort' is not defined"
+      "Empty input\n",
+      "One element\n",
+      "Two or more elements\n",
+      "Success: test_insertion_sort\n"
      ]
     }
    ],
    "source": [
     "%run -i test_insertion_sort.py"
    ]
-  },
-  {
-   "cell_type": "code",
-   "execution_count": null,
-   "metadata": {
-    "collapsed": true
-   },
-   "outputs": [],
-   "source": []
   }
  ],
  "metadata": {
@@ -206,7 +189,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.6"
+   "version": "2.7.10"
   }
  },
  "nbformat": 4,