fixed problems, new pull

arrays_strings/rotation/rotation_challenge.ipynb

@@ -34,7 +34,6 @@
    "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",
@@ -75,20 +74,38 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 5,
    "metadata": {
     "collapsed": false
    },
    "outputs": [],
    "source": [
-    "def is_substring(s1, s2):\n",
-    "    # TODO: Implement me\n",
-    "    pass\n",
+    "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",
     "\n",
     "def is_rotation(s1, s2):\n",
-    "    # TODO: Implement me\n",
-    "    # Call is_substring only once\n",
-    "    pass"
+    "    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)"
    ]
   },
   {
@@ -109,11 +126,19 @@
   },
   {
    "cell_type": "code",
-   "execution_count": null,
+   "execution_count": 6,
    "metadata": {
     "collapsed": false
    },
-   "outputs": [],
+   "outputs": [
+    {
+     "name": "stdout",
+     "output_type": "stream",
+     "text": [
+      "Success: test_rotation\n"
+     ]
+    }
+   ],
    "source": [
     "# %load test_rotation.py\n",
     "from nose.tools import assert_equal\n",
@@ -163,7 +188,7 @@
    "name": "python",
    "nbconvert_exporter": "python",
    "pygments_lexer": "ipython2",
-   "version": "2.7.10"
+   "version": "2.7.6"
   }
  },
  "nbformat": 4,