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   "source": [
    "This notebook was prepared by [Donne Martin](https://github.com/donnemartin). Source and license info is on [GitHub](https://github.com/donnemartin/interactive-coding-challenges)."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Challenge Notebook"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Problem: Implement an algorithm to have a robot move from the upper left corner to the bottom right corner of a grid.\n",
    "\n",
    "* [Constraints](#Constraints)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)\n",
    "* [Solution Notebook](#Solution-Notebook)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Constraints\n",
    "\n",
    "* Are there restrictions to how the robot moves?\n",
    "    * The robot can only move right and down\n",
    "* Are some cells off limits?\n",
    "    * Yes\n",
    "* Is this a rectangular grid? i.e. the grid is not jagged?\n",
    "    * Yes\n",
    "* Will there always be a valid way for the robot to get to the bottom right?\n",
    "    * No, return None\n",
    "* Can we assume the inputs are valid?\n",
    "    * No\n",
    "* Can we assume this fits memory?\n",
    "    * Yes"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Test Cases\n",
    "\n",
    "<pre>\n",
    "o = valid cell\n",
    "x = invalid cell\n",
    "\n",
    "   0  1  2  3\n",
    "0  o  o  o  o\n",
    "1  o  x  o  o\n",
    "2  o  o  x  o\n",
    "3  x  o  o  o\n",
    "4  o  o  x  o\n",
    "5  o  o  o  x\n",
    "6  o  x  o  x\n",
    "7  o  x  o  o\n",
    "</pre>\n",
    "\n",
    "* General case\n",
    "\n",
    "```\n",
    "expected = [(0, 0), (1, 0), (2, 0),\n",
    "            (2, 1), (3, 1), (4, 1),\n",
    "            (5, 1), (5, 2), (6, 2), \n",
    "            (7, 2), (7, 3)]\n",
    "```\n",
    "\n",
    "* No valid path: In above example, row 7 col 2 is also invalid -> None\n",
    "* None input -> None\n",
    "* Empty matrix -> None"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Algorithm\n",
    "\n",
    "Refer to the [Solution Notebook]().  If you are stuck and need a hint, the solution notebook's algorithm discussion might be a good place to start."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "class Grid(object):\n",
    "\n",
    "    def find_path(self, matrix):\n",
    "        # TODO: Implement me\n",
    "        pass"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "**The following unit test is expected to fail until you solve the challenge.**"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {
    "collapsed": false
   },
   "outputs": [],
   "source": [
    "# %load test_grid_path.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestGridPath(object):\n",
    "\n",
    "    def test_grid_path(self):\n",
    "        grid = Grid()\n",
    "        assert_equal(grid.find_path(None), None)\n",
    "        assert_equal(grid.find_path([[]]), None)\n",
    "        max_rows = 8\n",
    "        max_cols = 4\n",
    "        matrix = [[1] * max_cols for _ in range(max_rows)]\n",
    "        matrix[1][1] = 0\n",
    "        matrix[2][2] = 0\n",
    "        matrix[3][0] = 0\n",
    "        matrix[4][2] = 0\n",
    "        matrix[5][3] = 0\n",
    "        matrix[6][1] = 0\n",
    "        matrix[6][3] = 0\n",
    "        matrix[7][1] = 0\n",
    "        result = grid.find_path(matrix)\n",
    "        expected = [(0, 0), (1, 0), (2, 0),\n",
    "                    (2, 1), (3, 1), (4, 1),\n",
    "                    (5, 1), (5, 2), (6, 2), \n",
    "                    (7, 2), (7, 3)]\n",
    "        assert_equal(result, expected)\n",
    "        matrix[7][2] = 0\n",
    "        result = grid.find_path(matrix)\n",
    "        assert_equal(result, None)\n",
    "        print('Success: test_grid_path')\n",
    "\n",
    "\n",
    "def main():\n",
    "    test = TestGridPath()\n",
    "    test.test_grid_path()\n",
    "\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Solution Notebook\n",
    "\n",
    "Review the [Solution Notebook]() for a discussion on algorithms and code solutions."
   ]
  }
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