mirror of
https://github.com/donnemartin/interactive-coding-challenges.git
synced 2024-03-22 13:11:13 +08:00
Added an O(1) memory solution for the string rotation challenge
This commit is contained in:
Dan Monroe
parent
fe227a3fe3
commit
f10bdf45a8
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@ -77,9 +77,7 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": false
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},
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"metadata": {},
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"outputs": [],
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"source": [
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"class Rotation(object):\n",
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@ -113,9 +111,7 @@
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{
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"cell_type": "code",
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"execution_count": null,
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"metadata": {
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"collapsed": false
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},
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"metadata": {},
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"outputs": [],
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"source": [
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"# %load test_rotation.py\n",
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@ -124,19 +120,26 @@
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"\n",
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"class TestRotation(object):\n",
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"\n",
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" def test_rotation(self):\n",
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" rotation = Rotation()\n",
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" assert_equal(rotation.is_rotation('o', 'oo'), False)\n",
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" assert_equal(rotation.is_rotation(None, 'foo'), False)\n",
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" assert_equal(rotation.is_rotation('', 'foo'), False)\n",
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" assert_equal(rotation.is_rotation('', ''), True)\n",
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" assert_equal(rotation.is_rotation('foobarbaz', 'barbazfoo'), True)\n",
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" def test_rotation(self, func):\n",
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" assert_equal(func('o', 'oo'), False)\n",
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" assert_equal(func(None, 'foo'), False)\n",
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" assert_equal(func('', 'foo'), False)\n",
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" assert_equal(func('', ''), True)\n",
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" assert_equal(func('foobarbaz', 'barbazfoo'), True)\n",
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" print('Success: test_rotation')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestRotation()\n",
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" test.test_rotation()\n",
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" rotation = Rotation()\n",
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" test.test_rotation(rotation.is_rotation)\n",
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" try:\n",
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" rotation_in_place = RotationInPlace()\n",
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" test.test_rotation(rotation_in_place.is_rotation)\n",
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" except NameError:\n",
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" # Alternate solutions are only defined\n",
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" # in the solutions file\n",
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" pass\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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@ -169,9 +172,9 @@
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.0"
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"version": "3.5.2"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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"nbformat_minor": 1
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}
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@ -62,7 +62,7 @@
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Algorithm\n",
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"## Algorithm: Using the Python 'in' operation\n",
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"\n",
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"Examine the following test case:\n",
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"* s1 = 'barbazfoo'\n",
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@ -72,6 +72,10 @@
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"* s2 = 'foobarbaz'\n",
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"* s3 = 'barbaz*foobarbaz*foo'\n",
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"\n",
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"Notes:\n",
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"* When we concatenate the strings, we need to create a new one. This is why the extra space required is O(n).\n",
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"* However, this approach is very readable and concise, and using built-in Python collections operators is generally faster than writing your own, even if the theoretical time complexity is the same. Unless memory is constrained this is the better approach.\n",
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"\n",
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"Complexity:\n",
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"* Time: O(n)\n",
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"* Space: O(n)"
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@ -81,15 +85,13 @@
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code"
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"## Code: Using the Python 'in' operation"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {
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"collapsed": false
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},
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"metadata": {},
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"outputs": [],
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"source": [
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"class Rotation(object):\n",
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@ -109,15 +111,85 @@
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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"## Algorithm: Comparing In Place\n",
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"\n",
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"Notes:\n",
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"* This is taking the same high-level approach as the previous solution, but it is operating on the strings in place without creating any new string.\n",
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"* This is a bit more complex and less readable.\n",
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"* This approach is not using a built-in Python collection operator, so it will be slower.\n",
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"\n",
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"Complexity:\n",
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"* Time: O(n)\n",
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"* Space: O(1)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Code: Comparing In Place"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {
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"collapsed": false
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},
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"metadata": {},
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"outputs": [],
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"source": [
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"class RotationInPlace(object):\n",
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"\n",
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" def is_substring(self, s1, s2):\n",
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" # We already assured the strings are the same length; this is for readability\n",
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" length = len(s1)\n",
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"\n",
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" # If both strings are empty, they are trivially a rotation of one another\n",
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" if length == 0:\n",
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" return True\n",
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"\n",
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" i1, i2, matching_count = 0, 0, 0\n",
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" # This loop achieves the same as concatenating a string with itself\n",
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" for _ in range(2*length):\n",
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" \n",
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" # Count consecutive character matches.\n",
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" if s1[i1] == s2[i2]:\n",
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" matching_count += 1\n",
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" \n",
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" # If the count is equal to the length of the strings, we have found a rotation\n",
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" if matching_count == length:\n",
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" return True\n",
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" \n",
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" i2 += 1\n",
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" # If there is a mismatch, start the count over again\n",
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" else:\n",
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" matching_count, i2 = 0, 0\n",
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"\n",
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" # Increment i1 and wrap around if necessary\n",
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" i1 += 1\n",
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" if i1 == length:\n",
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" i1 = 0\n",
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" \n",
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" # Assume there is no rotation by default\n",
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" return False\n",
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"\n",
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" def is_rotation(self, s1, s2):\n",
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" if s1 is None or s2 is None:\n",
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" return False\n",
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" if len(s1) != len(s2):\n",
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" return False\n",
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" return self.is_substring(s1, s2)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Unit Test"
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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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@ -134,19 +206,26 @@
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"\n",
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"class TestRotation(object):\n",
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"\n",
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" def test_rotation(self):\n",
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" rotation = Rotation()\n",
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" assert_equal(rotation.is_rotation('o', 'oo'), False)\n",
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" assert_equal(rotation.is_rotation(None, 'foo'), False)\n",
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" assert_equal(rotation.is_rotation('', 'foo'), False)\n",
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" assert_equal(rotation.is_rotation('', ''), True)\n",
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" assert_equal(rotation.is_rotation('foobarbaz', 'barbazfoo'), True)\n",
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" def test_rotation(self, func):\n",
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" assert_equal(func('o', 'oo'), False)\n",
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" assert_equal(func(None, 'foo'), False)\n",
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" assert_equal(func('', 'foo'), False)\n",
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" assert_equal(func('', ''), True)\n",
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" assert_equal(func('foobarbaz', 'barbazfoo'), True)\n",
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" print('Success: test_rotation')\n",
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"\n",
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"\n",
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"def main():\n",
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" test = TestRotation()\n",
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" test.test_rotation()\n",
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" rotation = Rotation()\n",
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" test.test_rotation(rotation.is_rotation)\n",
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" try:\n",
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" rotation_in_place = RotationInPlace()\n",
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" test.test_rotation(rotation_in_place.is_rotation)\n",
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" except NameError:\n",
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" # Alternate solutions are only defined\n",
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" # in the solutions file\n",
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" pass\n",
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"\n",
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"\n",
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"if __name__ == '__main__':\n",
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@ -155,15 +234,14 @@
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {
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"collapsed": false
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},
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"execution_count": 4,
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"metadata": {},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Success: test_rotation\n",
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"Success: test_rotation\n"
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]
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}
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@ -175,23 +253,23 @@
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],
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"metadata": {
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"kernelspec": {
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"display_name": "Python 3",
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"display_name": "Python 2",
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"language": "python",
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"name": "python3"
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"name": "python2"
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},
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"language_info": {
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"codemirror_mode": {
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"name": "ipython",
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"version": 3
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"version": 2
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},
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"file_extension": ".py",
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"mimetype": "text/x-python",
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"name": "python",
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"nbconvert_exporter": "python",
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"pygments_lexer": "ipython3",
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"version": "3.5.0"
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"pygments_lexer": "ipython2",
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"version": "2.7.12"
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}
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},
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"nbformat": 4,
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"nbformat_minor": 0
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"nbformat_minor": 1
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}
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@ -3,19 +3,26 @@ from nose.tools import assert_equal
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class TestRotation(object):
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def test_rotation(self):
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rotation = Rotation()
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assert_equal(rotation.is_rotation('o', 'oo'), False)
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assert_equal(rotation.is_rotation(None, 'foo'), False)
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assert_equal(rotation.is_rotation('', 'foo'), False)
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assert_equal(rotation.is_rotation('', ''), True)
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assert_equal(rotation.is_rotation('foobarbaz', 'barbazfoo'), True)
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def test_rotation(self, func):
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assert_equal(func('o', 'oo'), False)
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assert_equal(func(None, 'foo'), False)
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assert_equal(func('', 'foo'), False)
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assert_equal(func('', ''), True)
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assert_equal(func('foobarbaz', 'barbazfoo'), True)
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print('Success: test_rotation')
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def main():
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test = TestRotation()
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test.test_rotation()
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rotation = Rotation()
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test.test_rotation(rotation.is_rotation)
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try:
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rotation_in_place = RotationInPlace()
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test.test_rotation(rotation_in_place.is_rotation)
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except NameError:
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# Alternate solutions are only defined
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# in the solutions file
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pass
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if __name__ == '__main__':
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