From f52450363b9835a67351edcd6b602490d24aab1f Mon Sep 17 00:00:00 2001
From: Donne Martin <donne.martin@gmail.com>
Date: Thu, 14 May 2015 07:34:35 -0400
Subject: [PATCH] Added method to return the length of a linked list.

---
 linked-lists/linked-list.ipynb | 43 +++++++++++++++++++++++++++++++++-
 linked-lists/linked_list.py    |  8 +++++++
 2 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/linked-lists/linked-list.ipynb b/linked-lists/linked-list.ipynb
index 91f74aa..d4b6f24 100644
--- a/linked-lists/linked-list.ipynb
+++ b/linked-lists/linked-list.ipynb
@@ -4,7 +4,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Problem: Implement a linked list with insert, append, find, delete, and print methods\n",
+    "## Problem: Implement a linked list with insert, append, find, delete, length, and print methods\n",
     "\n",
     "* [Clarifying Questions](#Clarifying-Questions)\n",
     "* [Test Cases](#Test-Cases)\n",
@@ -60,6 +60,10 @@
     "* Delete in a list with one element or more matching elements\n",
     "* Delete in a list with no matches\n",
     "\n",
+    "### Length\n",
+    "\n",
+    "* Length of zero or more elements\n",
+    "\n",
     "### Print\n",
     "\n",
     "* Print an empty list\n",
@@ -126,6 +130,15 @@
     "* Time: O(n)\n",
     "* Space: In-place\n",
     "\n",
+    "### Length\n",
+    "\n",
+    "* For each node\n",
+    "    * Increase length counter\n",
+    "    \n",
+    "Complexity:\n",
+    "* Time: O(n)\n",
+    "* Space: In-place\n",
+    "\n",
     "### Print\n",
     "\n",
     "* For each node\n",
@@ -164,6 +177,14 @@
     "class LinkedList(object):\n",
     "    def __init__(self, head=None):\n",
     "        self.head = head\n",
+    "\n",
+    "    def __len__(self):\n",
+    "        curr = self.head\n",
+    "        counter = 0\n",
+    "        while curr is not None:\n",
+    "            counter += 1\n",
+    "            curr = curr.next\n",
+    "        return counter\n",
     "    \n",
     "    def insert_to_front(self, data):\n",
     "        if data is None:\n",
@@ -335,6 +356,26 @@
     "linked_list.delete('aa')"
    ]
   },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {
+    "collapsed": false
+   },
+   "outputs": [],
+   "source": [
+    "# Test length\n",
+    "# Zero elements\n",
+    "linked_list = LinkedList(None)\n",
+    "print(len(linked_list))\n",
+    "# One or more elements\n",
+    "head = Node(10)\n",
+    "linked_list = LinkedList(head)\n",
+    "linked_list.insert_to_front('a')\n",
+    "linked_list.insert_to_front('bc')\n",
+    "print(len(linked_list))"
+   ]
+  },
   {
    "cell_type": "code",
    "execution_count": null,
diff --git a/linked-lists/linked_list.py b/linked-lists/linked_list.py
index cce8a2e..e27e97b 100644
--- a/linked-lists/linked_list.py
+++ b/linked-lists/linked_list.py
@@ -10,6 +10,14 @@ class Node(object):
 class LinkedList(object):
     def __init__(self, head=None):
         self.head = head
+
+    def __len__(self):
+        curr = self.head
+        counter = 0
+        while curr is not None:
+            counter += 1
+            curr = curr.next
+        return counter
     
     def insert_to_front(self, data):
         if data is None: