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Reworked notebook: Added more detail to clarifying questions and test cases. Reworked algorithm discussion, code, and unit test.

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Donne Martin 2015-06-24 18:23:27 -04:00
parent 88935b61f0
commit 6cea5d003a
1 changed files with 61 additions and 41 deletions
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102
arrays-strings/replace_char.ipynb
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@ -17,7 +17,8 @@
"* [Test Cases](#Test-Cases)\n",
"* [Algorithm](#Algorithm)\n",
"* [Code](#Code)\n",
"* [Pythonic-Code: Not In-Place](#Pythonic-Code:-Not-In-Place)"
"* [Pythonic-Code: Not In-Place](#Pythonic-Code:-Not-In-Place)\n",
"* [Unit Test](#Unit-Test)"
]
},
{
@ -26,8 +27,11 @@
"source": [
"## Clarifying Questions\n",
"\n",
"* Is the string ASCII (extended)? Or Unicode?\n",
" * ASCII extended, which is 256 characters\n",
"*Problem statements are sometimes intentionally ambiguous. Asking clarifying questions, identifying constraints, and stating assumptions 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",
"* Is there enough space in the data structure for this operation?\n",
" * Yes"
]
@ -38,49 +42,21 @@
"source": [
"## Test Cases\n",
"\n",
"*Identifying and running through general and edge cases are important. You generally will not be asked to write a unit test like what is shown below.*\n",
"\n",
"* NULL->NULL\n",
"* ' ' -> '%20'\n",
"* ' foo bar ' -> '%20foo%20bar%20'\n",
"* 'foo' -> 'foo'"
]
},
{
"cell_type": "code",
"execution_count": null,
"metadata": {
"collapsed": true
},
"outputs": [],
"source": [
"from nose.tools import assert_equal\n",
"\n",
"class Test(object):\n",
" def test_replace_char(self, func):\n",
" str0 = None\n",
" str1 = bytearray(' ||')\n",
" str2 = bytearray(' foo bar ||||||')\n",
" str3 = bytearray('foo')\n",
" func(str0, 0)\n",
" func(str1, 1)\n",
" func(str2, 9)\n",
" func(str3, 3)\n",
" assert_equal(str0, None)\n",
" assert_equal(str1, '%20')\n",
" assert_equal(str2, '%20foo%20bar%20')\n",
" assert_equal(str3, 'foo')\n",
"\n",
"def run_tests(func):\n",
" test = Test()\n",
" test.test_replace_char(func)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Algorithm\n",
"\n",
"Since Python strings are immutable, we'll use a bytearray instead to exercise in-place string manipulation as you would get with a C string (which is null terminated, as seen in the diagram below). For the python bytearray we will not use a null terminator.\n",
"Since Python strings are immutable, we'll use a bytearray instead to exercise in-place string manipulation as you would get with a C string (which is null terminated, as seen in the diagram below). Python does not use a null-terminator.\n",
"\n",
"![alt text](https://raw.githubusercontent.com/donnemartin/algorithms-data-structures/master/images/replace_string.jpg)\n",
"\n",
@ -110,7 +86,7 @@
},
{
"cell_type": "code",
"execution_count": null,
"execution_count": 1,
"metadata": {
"collapsed": false
},
@ -124,14 +100,12 @@
" for i in xrange(length-1, -1, -1):\n",
" if chr(string[i]) == ' ':\n",
" string[new_length] = '0'\n",
" string[new_length - 1] = '2'\n",
" string[new_length - 2] = '%'\n",
" string[new_length-1] = '2'\n",
" string[new_length-2] = '%'\n",
" new_length -= 3\n",
" else:\n",
" string[new_length] = string[i]\n",
" new_length -= 1\n",
"\n",
"run_tests(encode_spaces)"
" new_length -= 1"
]
},
{
@ -145,7 +119,7 @@
},
{
"cell_type": "code",
"execution_count": null,
"execution_count": 2,
"metadata": {
"collapsed": false
},
@ -159,6 +133,52 @@
"def encode_spaces_alt2(string):\n",
" return string.replace(' ', '%20')"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Unit Test"
]
},
{
"cell_type": "code",
"execution_count": 3,
"metadata": {
"collapsed": false
},
"outputs": [
{
"name": "stdout",
"output_type": "stream",
"text": [
"Success: test_replace_char\n"
]
}
],
"source": [
"from nose.tools import assert_equal\n",
"\n",
"class Test(object):\n",
" def test_replace_char(self, func):\n",
" str0 = None\n",
" str1 = bytearray(' ||')\n",
" str2 = bytearray(' foo bar ||||||')\n",
" str3 = bytearray('foo')\n",
" func(str0, 0)\n",
" func(str1, 1)\n",
" func(str2, 9)\n",
" func(str3, 3)\n",
" assert_equal(str0, None)\n",
" assert_equal(str1, '%20')\n",
" assert_equal(str2, '%20foo%20bar%20')\n",
" assert_equal(str3, 'foo')\n",
" print('Success: test_replace_char')\n",
"\n",
"if __name__ == '__main__':\n",
" test = Test()\n",
" test.test_replace_char(encode_spaces)"
]
}
],
"metadata": {