From 90f75050189d3ae3de7ce8846ec152c7624a502d Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Sun, 12 Jun 2016 23:27:36 -0400
Subject: [PATCH] Polish kth to last element challenge and solution

Update algorithm discussion and solution.
---
 .../kth_to_last_elem_challenge.ipynb          | 10 ++--
 .../kth_to_last_elem_solution.ipynb           | 49 +++++++++----------
 2 files changed, 28 insertions(+), 31 deletions(-)

diff --git a/linked_lists/kth_to_last_elem/kth_to_last_elem_challenge.ipynb b/linked_lists/kth_to_last_elem/kth_to_last_elem_challenge.ipynb
index 2d8d398..071a87c 100644
--- a/linked_lists/kth_to_last_elem/kth_to_last_elem_challenge.ipynb
+++ b/linked_lists/kth_to_last_elem/kth_to_last_elem_challenge.ipynb
@@ -175,21 +175,21 @@
  ],
  "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": "3.5.0"
   }
  },
  "nbformat": 4,
diff --git a/linked_lists/kth_to_last_elem/kth_to_last_elem_solution.ipynb b/linked_lists/kth_to_last_elem/kth_to_last_elem_solution.ipynb
index 57b05b6..e5a2774 100644
--- a/linked_lists/kth_to_last_elem/kth_to_last_elem_solution.ipynb
+++ b/linked_lists/kth_to_last_elem/kth_to_last_elem_solution.ipynb
@@ -63,10 +63,10 @@
    "source": [
     "## Algorithm\n",
     "\n",
-    "* Setup two pointers, current and previous\n",
-    "* Give current a headstart, incrementing it once if k = 1, twice if k = 2, ...\n",
-    "* Increment both pointers until current reaches the end\n",
-    "* Return the value of previous\n",
+    "* Setup two pointers, fast and slow\n",
+    "* Give fast a headstart, incrementing it once if k = 1, twice if k = 2, ...\n",
+    "* Increment both pointers until fast reaches the end\n",
+    "* Return the value of slow\n",
     "\n",
     "Complexity:\n",
     "* Time: O(n)\n",
@@ -103,26 +103,23 @@
     "\n",
     "    def kth_to_last_elem(self, k):\n",
     "        if self.head is None:\n",
-    "            return\n",
-    "        if k >= len(self):\n",
-    "            return\n",
-    "        curr = self.head\n",
-    "        prev = self.head\n",
-    "        counter = 0\n",
+    "            return None\n",
+    "        fast = self.head\n",
+    "        slow = self.head\n",
     "\n",
-    "        # Give current a headstart, incrementing it\n",
+    "        # Give fast a headstart, incrementing it\n",
     "        # once for k = 1, twice for k = 2, etc\n",
-    "        while counter < k:\n",
-    "            curr = curr.next\n",
-    "            counter += 1\n",
-    "            if curr is None:\n",
-    "                return\n",
+    "        for _ in range(k):\n",
+    "            fast = fast.next\n",
+    "            # If k >= num elements, return None\n",
+    "            if fast is None:\n",
+    "                return None\n",
     "\n",
-    "        # Increment both pointers until current reaches the end\n",
-    "        while curr.next is not None:\n",
-    "            curr = curr.next\n",
-    "            prev = prev.next\n",
-    "        return prev.data"
+    "        # Increment both pointers until fast reaches the end\n",
+    "        while fast.next is not None:\n",
+    "            fast = fast.next\n",
+    "            slow = slow.next\n",
+    "        return slow.data"
    ]
   },
   {
@@ -212,21 +209,21 @@
  ],
  "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": "3.5.0"
   }
  },
  "nbformat": 4,