interactive-coding-challenges/linked_lists/delete_mid/delete_mid_solution.ipynb

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   "source": [
    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges).</i></small>"
   ]
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   "source": [
    "# Solution Notebook"
   ]
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   "source": [
    "## Problem: Delete a node in the middle, given only access to that node.\n",
    "\n",
    "* [Constraints](#Constraints)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)"
   ]
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   "cell_type": "markdown",
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   "source": [
    "## Constraints\n",
    "\n",
    "*Problem statements are sometimes ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
    "\n",
    "* What if the final node is being deleted, for example a single node list?  Do we make it a dummy with a NULL value?\n",
    "    * Yes\n",
    "* Can we assume we already have a linked list class that can be used for this problem?\n",
    "    * Yes"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "* Delete on empty list -> None\n",
    "* Delete None -> None\n",
    "* Delete on one node -> [None]\n",
    "* Delete on multiple nodes"
   ]
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    "## Algorithm\n",
    "\n",
    "We'll need two pointers, one to the current node and one to the next node.  We will copy the next node's data to the current node's data (effectively deleting the current node) and update the current node's next pointer.\n",
    "\n",
    "* Check for error cases listed above\n",
    "* set curr.data to next.data\n",
    "* set curr.next to next.next\n",
    "\n",
    "Complexity:\n",
    "* Time: O(1)\n",
    "* Space: In-place"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
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  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {
    "collapsed": false
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   "outputs": [],
   "source": [
    "%run ../linked_list/linked_list.py"
   ]
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  {
   "cell_type": "code",
   "execution_count": 2,
   "metadata": {
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   "outputs": [],
   "source": [
    "class MyLinkedList(LinkedList):\n",
    "    \n",
    "    def delete_node(self, node):\n",
    "        if self.head is None:\n",
    "            return\n",
    "        if node is None:\n",
    "            return\n",
    "        node_next = node.next\n",
    "        if node_next is None:\n",
    "            node.data = None\n",
    "            node.next = None\n",
    "        else:\n",
    "            node.data = node_next.data\n",
    "            node.next = node_next.next"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
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  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {
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   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Overwriting test_delete_mid.py\n"
     ]
    }
   ],
   "source": [
    "%%writefile test_delete_mid.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestDeleteNode(object):\n",
    "    \n",
    "    def test_delete_node(self):\n",
    "        print('Test: Empty list, null node to delete')\n",
    "        linked_list = MyLinkedList(None)\n",
    "        linked_list.delete_node(None)\n",
    "        assert_equal(linked_list.get_all_data(), [])\n",
    "\n",
    "        print('Test: One node')\n",
    "        head = Node(2)\n",
    "        linked_list = MyLinkedList(head)\n",
    "        linked_list.delete_node(head)\n",
    "        assert_equal(linked_list.get_all_data(), [None])\n",
    "\n",
    "        print('Test: Multiple nodes')\n",
    "        linked_list = MyLinkedList(None)        \n",
    "        node0 = linked_list.insert_to_front(1)\n",
    "        node1 = linked_list.insert_to_front(3)\n",
    "        node2 = linked_list.insert_to_front(4)\n",
    "        node3 = linked_list.insert_to_front(1)\n",
    "        linked_list.delete_node(node2)\n",
    "        assert_equal(linked_list.get_all_data(), [1, 3, 1])\n",
    "        \n",
    "        print('Success: test_delete_node')\n",
    "\n",
    "def main():\n",
    "    test = TestDeleteNode()\n",
    "    test.test_delete_node()\n",
    "    \n",
    "if __name__ == '__main__':\n",
    "    main()"
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   "cell_type": "code",
   "execution_count": 4,
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     "name": "stdout",
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     "text": [
      "Test: Empty list, null node to delete\n",
      "Test: One node\n",
      "Test: Multiple nodes\n",
      "Success: test_delete_node\n"
     ]
    }
   ],
   "source": [
    "%run -i test_delete_mid.py"
   ]
  }
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