diff --git a/arrays_strings/permutation/permutation_challenge.ipynb b/arrays_strings/permutation/permutation_challenge.ipynb
new file mode 100644
index 0000000..9b6d371
--- /dev/null
+++ b/arrays_strings/permutation/permutation_challenge.ipynb
@@ -0,0 +1,171 @@
+{
+ "cells": [
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Challenge Notebook"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Problem: Determine if a string is a permutation of another string\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",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "\n",
+    "* Can we assume the string is ASCII?\n",
+    "    * Yes\n",
+    "    * Note: Unicode strings could require special handling depending on your language\n",
+    "* Is whitespace important?\n",
+    "    * Yes\n",
+    "* Is this case sensitive?  'Nib', 'bin' is not a match?\n",
+    "    * Yes"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Test Cases\n",
+    "\n",
+    "* One or more empty strings -> False\n",
+    "* 'Nib', 'bin' -> False\n",
+    "* 'act', 'cat' -> True\n",
+    "* 'a ct', 'ca t' -> True"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Algorithm\n",
+    "\n",
+    "Refer to the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/arrays_strings/permutation/permutation_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": false
+   },
+   "outputs": [],
+   "source": [
+    "def permutations(str1, str2):\n",
+    "    # TODO: Implement me\n",
+    "    pass"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Unit Test"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "\n",
+    "\n",
+    "**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_permutation_solution.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestPermutation(object):\n",
+    "    \n",
+    "    def test_permutation(self, func):\n",
+    "        assert_equal(func('', 'foo'), False)\n",
+    "        assert_equal(func('Nib', 'bin'), False)\n",
+    "        assert_equal(func('act', 'cat'), True)\n",
+    "        assert_equal(func('a ct', 'ca t'), True)\n",
+    "        print('Success: test_permutation')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestPermutation()\n",
+    "    test.test_permutation(permutations)\n",
+    "    try:\n",
+    "        test.test_permutation(permutations_alt)\n",
+    "    except NameError:\n",
+    "        # Alternate solutions are only defined\n",
+    "        # in the solutions file\n",
+    "        pass\n",
+    "    \n",
+    "if __name__ == '__main__':\n",
+    "    main()"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "## Solution Notebook\n",
+    "\n",
+    "Review the [Solution Notebook](http://nbviewer.ipython.org/github/donnemartin/coding-challenges/blob/master/arrays_strings/permutation/permutation_solution.ipynb) for a discussion on algorithms and code solutions."
+   ]
+  }
+ ],
+ "metadata": {
+  "kernelspec": {
+   "display_name": "Python 2",
+   "language": "python",
+   "name": "python2"
+  },
+  "language_info": {
+   "codemirror_mode": {
+    "name": "ipython",
+    "version": 2
+   },
+   "file_extension": ".py",
+   "mimetype": "text/x-python",
+   "name": "python",
+   "nbconvert_exporter": "python",
+   "pygments_lexer": "ipython2",
+   "version": "2.7.10"
+  }
+ },
+ "nbformat": 4,
+ "nbformat_minor": 0
+}
diff --git a/arrays_strings/permutation/permutation_solution.ipynb b/arrays_strings/permutation/permutation_solution.ipynb
index 57a25f3..e60608b 100644
--- a/arrays_strings/permutation/permutation_solution.ipynb
+++ b/arrays_strings/permutation/permutation_solution.ipynb
@@ -4,7 +4,14 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</i></small>"
+    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/coding-challenges).</i></small>"
+   ]
+  },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "# Solution Notebook"
    ]
   },
   {
@@ -28,9 +35,9 @@
    "source": [
     "## Constraints\n",
     "\n",
-    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
+    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
     "\n",
-    "* Can I assume the string is ASCII?\n",
+    "* Can we assume the string is ASCII?\n",
     "    * Yes\n",
     "    * Note: Unicode strings could require special handling depending on your language\n",
     "* Is whitespace important?\n",
@@ -110,7 +117,7 @@
     "Notes:\n",
     "* Since the characters are in ASCII, we could potentially use an array of size 128 (or 256 for extended ASCII), where each array index is equivalent to an ASCII value\n",
     "* Instead of using two hash maps, you could use one hash map and increment character values based on the first string and decrement based on the second string\n",
-    "* You can short circuit if the lengths of each string are not equal, len() in Python is generally O(1)\n",
+    "* You can short circuit if the lengths of each string are not equal, although len() in Python is generally O(1) unlike other languages like C where getting the length of a string is O(n)\n",
     "\n",
     "Complexity:\n",
     "* Time: O(n)\n",
@@ -134,6 +141,7 @@
    "source": [
     "from collections import defaultdict\n",
     "\n",
+    "\n",
     "def unique_counts(string):\n",
     "    dict_chars = defaultdict(int)\n",
     "    for char in string:\n",
@@ -156,15 +164,51 @@
    ]
   },
   {
-   "cell_type": "markdown",
-   "metadata": {},
+   "cell_type": "code",
+   "execution_count": 3,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Overwriting test_permutation_solution.py\n"
+     ]
+    }
+   ],
    "source": [
-    "*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.*"
+    "%%writefile test_permutation_solution.py\n",
+    "from nose.tools import assert_equal\n",
+    "\n",
+    "\n",
+    "class TestPermutation(object):\n",
+    "    \n",
+    "    def test_permutation(self, func):\n",
+    "        assert_equal(func('', 'foo'), False)\n",
+    "        assert_equal(func('Nib', 'bin'), False)\n",
+    "        assert_equal(func('act', 'cat'), True)\n",
+    "        assert_equal(func('a ct', 'ca t'), True)\n",
+    "        print('Success: test_permutation')\n",
+    "\n",
+    "def main():\n",
+    "    test = TestPermutation()\n",
+    "    test.test_permutation(permutations)\n",
+    "    try:\n",
+    "        test.test_permutation(permutations_alt)\n",
+    "    except NameError:\n",
+    "        # Alternate solutions are only defined\n",
+    "        # in the solutions file\n",
+    "        pass\n",
+    "    \n",
+    "if __name__ == '__main__':\n",
+    "    main()"
    ]
   },
   {
    "cell_type": "code",
-   "execution_count": 3,
+   "execution_count": 4,
    "metadata": {
     "collapsed": false
    },
@@ -179,20 +223,7 @@
     }
    ],
    "source": [
-    "from nose.tools import assert_equal\n",
-    "\n",
-    "class Test(object):\n",
-    "    def test_permutation(self, func):\n",
-    "        assert_equal(func('', 'foo'), False)\n",
-    "        assert_equal(func('Nib', 'bin'), False)\n",
-    "        assert_equal(func('act', 'cat'), True)\n",
-    "        assert_equal(func('a ct', 'ca t'), True)\n",
-    "        print('Success: test_permutation')\n",
-    "\n",
-    "if __name__ == '__main__':\n",
-    "    test = Test()\n",
-    "    test.test_permutation(permutations)\n",
-    "    test.test_permutation(permutations_alt)"
+    "run -i test_permutation_solution.py"
    ]
   }
  ],
diff --git a/arrays_strings/permutation/test_permutation_solution.py b/arrays_strings/permutation/test_permutation_solution.py
new file mode 100644
index 0000000..430fa81
--- /dev/null
+++ b/arrays_strings/permutation/test_permutation_solution.py
@@ -0,0 +1,24 @@
+from nose.tools import assert_equal
+
+
+class TestPermutation(object):
+    
+    def test_permutation(self, func):
+        assert_equal(func('', 'foo'), False)
+        assert_equal(func('Nib', 'bin'), False)
+        assert_equal(func('act', 'cat'), True)
+        assert_equal(func('a ct', 'ca t'), True)
+        print('Success: test_permutation')
+
+def main():
+    test = TestPermutation()
+    test.test_permutation(permutations)
+    try:
+        test.test_permutation(permutations_alt)
+    except NameError:
+        # Alternate solutions are only defined
+        # in the solutions file
+        pass
+    
+if __name__ == '__main__':
+    main()
\ No newline at end of file