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    "## 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",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Clarifying Questions\n",
    "\n",
    "* Is this a singly or doubly linked list?\n",
    "    * Singly\n",
    "* Is this a circular list?\n",
    "    * No\n",
    "* Do we keep track of the tail or just the head?\n",
    "    * Just the head"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "### Insert to Front\n",
    "\n",
    "* Insert a NULL\n",
    "* Insert in an empty list\n",
    "* Insert in a list with one element or more elements\n",
    "\n",
    "### Append\n",
    "\n",
    "* Append a NULL\n",
    "* Append in an empty list\n",
    "* Insert in a list with one element or more elements\n",
    "\n",
    "### Find\n",
    "\n",
    "* Find a NULL\n",
    "* Find in an empty list\n",
    "* Find in a list with one element or more matching elements\n",
    "* Find in a list with no matches\n",
    "\n",
    "### Delete\n",
    "\n",
    "* Delete a NULL\n",
    "* Delete in an empty list\n",
    "* 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",
    "* Print a list with one or more elements"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "### Insert to Front\n",
    "\n",
    "* If the data we are inserting is NULL, return\n",
    "* Create a node with the input data\n",
    "* If this is an empty list\n",
    "    * Assign the head to the node\n",
    "* Else\n",
    "    * Set the node.next to the head\n",
    "    * Set the head to the node\n",
    "\n",
    "Complexity:\n",
    "* Time: O(1)\n",
    "* Space: O(1), a new node is added\n",
    "\n",
    "### Append\n",
    "\n",
    "* If the data we are inserting is NULL, return\n",
    "* Create a node with the input data\n",
    "* If this is an empty list\n",
    "    * Assign the head to the node\n",
    "* Else\n",
    "    * Iterate to the end of the list\n",
    "    * Set the final node's next to the new node\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: O(1), a new node is added\n",
    "\n",
    "### Find\n",
    "\n",
    "* If data we are finding is NULL, return\n",
    "* If the list is empty, return\n",
    "* For each node\n",
    "    * If the value is a match, return it\n",
    "    * Else, move on to the next node\n",
    "\n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: In-place\n",
    "\n",
    "### Delete\n",
    "\n",
    "* If data we are deleting is NULL, return\n",
    "* If the list is empty, return\n",
    "* For each node, keep track of previous and current node\n",
    "    * If the value we are deleting is a match in the current node\n",
    "        * Update previous node's next pointer to the current node's next pointer\n",
    "        * We do not have have to explicitly delete in Python\n",
    "    * Else, move on to the next node\n",
    "\n",
    "Complexity:\n",
    "* 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",
    "    * Print the node's value\n",
    "    \n",
    "Complexity:\n",
    "* Time: O(n)\n",
    "* Space: In-place"
   ]
  },
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   "metadata": {},
   "source": [
    "## Code"
   ]
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   "source": [
    "%%writefile linked_list.py\n",
    "\n",
    "class Node(object):\n",
    "    def __init__(self, data, next_node=None):\n",
    "        self.next = next_node\n",
    "        self.data = data\n",
    "        \n",
    "    def __str__(self):\n",
    "        return self.data\n",
    "\n",
    "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",
    "            return\n",
    "        node = Node(data)\n",
    "        if self.head is None:\n",
    "            self.head = node\n",
    "        else:\n",
    "            node.next = self.head\n",
    "            self.head = node\n",
    "            \n",
    "    def append(self, data, next_node=None):\n",
    "        if data is None:\n",
    "            return\n",
    "        node = Node(data, next_node)\n",
    "        if self.head is None:\n",
    "            self.head = node\n",
    "        else:\n",
    "            curr_node = self.head\n",
    "            while curr_node.next is not None:\n",
    "                curr_node = curr_node.next\n",
    "            curr_node.next = node\n",
    "            \n",
    "    def find(self, data):\n",
    "        if data is None:\n",
    "            return\n",
    "        if self.head is None:\n",
    "            return\n",
    "        curr_node = self.head\n",
    "        while curr_node is not None:\n",
    "            if curr_node.data == data:\n",
    "                return curr_node\n",
    "            else:\n",
    "                curr_node = curr_node.next\n",
    "                \n",
    "    def delete(self, data):\n",
    "        if data is None:\n",
    "            return\n",
    "        if self.head is None:\n",
    "            return\n",
    "        prev_node = self.head\n",
    "        curr_node = prev_node.next\n",
    "        while curr_node is not None:\n",
    "            if curr_node.data == data:\n",
    "                prev_node.next = curr_node.next\n",
    "                return\n",
    "            else:\n",
    "                prev_node = curr_node\n",
    "                curr_node = curr_node.next\n",
    "\n",
    "    def print_list(self):\n",
    "        curr_node = self.head\n",
    "        while curr_node is not None:\n",
    "            print(curr_node.data)\n",
    "            curr_node = curr_node.next"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": true
   },
   "outputs": [],
   "source": [
    "%run linked_list.py"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
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   },
   "outputs": [],
   "source": [
    "# Test insert_to_front\n",
    "# Insert in an empty list\n",
    "linked_list = LinkedList(None)\n",
    "linked_list.insert_to_front(10)\n",
    "linked_list.print_list()\n",
    "# Insert a NULL\n",
    "linked_list.insert_to_front(None)\n",
    "linked_list.print_list()\n",
    "# Insert in a list with one element or more elements\n",
    "linked_list.insert_to_front('a')\n",
    "linked_list.insert_to_front('bc')\n",
    "linked_list.print_list()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
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   },
   "outputs": [],
   "source": [
    "# Test append\n",
    "# Insert in an empty list\n",
    "linked_list = LinkedList(None)\n",
    "linked_list.append(10)\n",
    "linked_list.print_list()\n",
    "# Insert a NULL\n",
    "linked_list.append(None)\n",
    "linked_list.print_list()\n",
    "# Insert in a list with one element or more elements\n",
    "linked_list.append('a')\n",
    "linked_list.append('bc')\n",
    "linked_list.print_list()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Test find\n",
    "# Find in an empty list\n",
    "linked_list = LinkedList(None)\n",
    "node = linked_list.find('a')\n",
    "print(node)\n",
    "# Find a NULL\n",
    "head = Node(10)\n",
    "linked_list = LinkedList(head)\n",
    "node = linked_list.find(None)\n",
    "print(node)\n",
    "# Find in a list with one element or more matching 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",
    "node = linked_list.find('a')\n",
    "print(node)\n",
    "# Find in a list with no matches\n",
    "node = linked_list.find('aaa')\n",
    "print(node)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Test delete\n",
    "# Delete in an empty list\n",
    "linked_list = LinkedList(None)\n",
    "linked_list.delete('a')\n",
    "linked_list.print_list()\n",
    "# Delete a NULL\n",
    "head = Node(10)\n",
    "linked_list = LinkedList(head)\n",
    "linked_list.delete(None)\n",
    "linked_list.print_list()\n",
    "# Delete in a list with one element or more matching 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",
    "linked_list.delete('a')\n",
    "linked_list.print_list()\n",
    "# Delete in a list with no matches\n",
    "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,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# Test empty print\n",
    "linked_list = LinkedList(None)\n",
    "linked_list.print_list()"
   ]
  }
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