interactive-coding-challenges/arrays_strings/rotation/rotation_challenge.ipynb

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    "<small><i>This notebook was prepared by [Donne Martin](http://donnemartin.com). Source and license info is on [GitHub](https://bit.ly/code-notes).</i></small>"
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    "## Problem: Determine if a string s1 is a rotation of another string s2, by calling (only once) a function is_substring\n",
    "\n",
    "* [Constraints and Assumptions](#Constraints-and-Assumptions)\n",
    "* [Test Cases](#Test-Cases)\n",
    "* [Algorithm](#Algorithm)\n",
    "* [Code](#Code)\n",
    "* [Unit Test](#Unit-Test)"
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    "## Constraints\n",
    "\n",
    "*Problem statements are often intentionally ambiguous.  Identifying constraints and stating assumptions can help to ensure you code the intended solution.*\n",
    "\n",
    "* Can I assume the string is ASCII?\n",
    "    * Yes\n",
    "    * Note: Unicode strings could require special handling depending on your language\n",
    "* Can you use additional data structures?  \n",
    "    * Yes\n",
    "* Is this case sensitive?\n",
    "    * Yes"
   ]
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   "source": [
    "## Test Cases\n",
    "\n",
    "* Any strings that differ in size -> False\n",
    "* None, 'foo' -> False (any None results in False)\n",
    "* ' ', 'foo' -> False\n",
    "* ' ', ' ' -> True\n",
    "* 'foobarbaz', 'barbazfoo' -> True"
   ]
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   "cell_type": "markdown",
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   "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."
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Code"
   ]
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   "source": [
    "def is_substring(s1, s2):\n",
    "    # TODO: Implement me\n",
    "    pass\n",
    "\n",
    "def is_rotation(s1, s2):\n",
    "    # TODO: Implement me\n",
    "    # Call is_substring only once\n",
    "    pass"
   ]
  },
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Unit Test"
   ]
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   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "*It is important to identify and run through general and edge cases from the [Test Cases](#Test-Cases) section by hand.  You generally will not be asked to write a unit test like what is shown below.*\n",
    "\n",
    "**The following unit test is expected to fail until you solve the challenge.**"
   ]
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   "source": [
    "# %load test_rotation.py\n",
    "from nose.tools import assert_equal\n",
    "\n",
    "\n",
    "class TestRotation(object):\n",
    "    \n",
    "    def test_rotation(self):\n",
    "        assert_equal(is_rotation('o', 'oo'), False)\n",
    "        assert_equal(is_rotation(None, 'foo'), False)\n",
    "        assert_equal(is_rotation('', 'foo'), False)\n",
    "        assert_equal(is_rotation('', ''), True)\n",
    "        assert_equal(is_rotation('foobarbaz', 'barbazfoo'), True)\n",
    "        print('Success: test_rotation')\n",
    "\n",
    "def main():\n",
    "    test = TestRotation()\n",
    "    test.test_rotation()\n",
    "\n",
    "if __name__ == '__main__':\n",
    "    main()"
   ]
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