Polish permutation challenge and solution

arrays_strings/permutation/permutation_challenge.ipynb

@@ -40,6 +40,10 @@
     "* Is whitespace important?\n",
     "    * Yes\n",
     "* Is this case sensitive?  'Nib', 'bin' is not a match?\n",
+    "    * Yes\n",
+    "* Can we use additional data structures?\n",
+    "    * Yes\n",
+    "* Can we assume this fits in memory?\n",
     "    * Yes"
    ]
   },
@@ -49,6 +53,7 @@
    "source": [
     "## Test Cases\n",
     "\n",
+    "* One or more None inputs -> False\n",
     "* One or more empty strings -> False\n",
     "* 'Nib', 'bin' -> False\n",
     "* 'act', 'cat' -> True\n",
@@ -115,6 +120,7 @@
     "class TestPermutation(object):\n",
     "\n",
     "    def test_permutation(self, func):\n",
+    "        assert_equal(func(None, 'foo'), False)\n",
     "        assert_equal(func('', 'foo'), False)\n",
     "        assert_equal(func('Nib', 'bin'), False)\n",
     "        assert_equal(func('act', 'cat'), True)\n",
@@ -149,21 +155,21 @@
  ],
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-   "display_name": "Python 2",
+   "display_name": "Python 3",
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-   "name": "python2"
+   "name": "python3"
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   "language_info": {
    "codemirror_mode": {
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-    "version": 2
+    "version": 3
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    "name": "python",
    "nbconvert_exporter": "python",
-   "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "pygments_lexer": "ipython3",
+   "version": "3.5.0"
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