Update str diff solution

Update constraints, test cases, and dictionary solution. Fix inconsistencies between challenge and solution notebooks.

Author: donnemartin

arrays_strings/str_diff/str_diff_challenge.ipynb

@@ -34,13 +34,13 @@
  "source": [
  "## Constraints\n",
  "\n",
- "* Assume two strings str1, str2, where str2 contains the same set of characters in str1 with one additional character.\n",
  "* Can we assume the strings are ASCII?\n",
  " * Yes\n",
  "* Is case important?\n",
  " * The strings are lower case\n",
  "* Can we assume the inputs are valid?\n",
  " * No, check for None\n",
+ " * Otherwise, assume there is only a single different char between the two strings\n",
  "* Can we assume this fits memory?\n",
  " * Yes"
  ]
@@ -52,6 +52,8 @@
  "## Test Cases\n",
  "\n",
  "* None input -> TypeError\n",
+ "* 'ab', 'aab' -> 'a'\n",
+ "* 'aab', 'ab' -> 'a'\n",
  "* 'abcd', 'abcde' -> 'e'\n",
  "* 'aaabbcdd', 'abdbacade' -> 'e'"
  ]
@@ -82,7 +84,7 @@
  "source": [
  "class Solution(object):\n",
  "\n",
- " def find_diff(self, s, t):\n",
+ " def find_diff(self, str1, str2):\n",
  " # TODO: Implement me\n",
  " pass"
  ]
@@ -117,9 +119,15 @@
  "\n",
  " def test_find_diff(self):\n",
  " solution = Solution()\n",
- " assert_raises(TypeError, solution.find_diff, None, None)\n",
+ " assert_raises(TypeError, solution.find_diff, None)\n",
+ " assert_equal(solution.find_diff('ab', 'aab'), 'a')\n",
+ " assert_equal(solution.find_diff('aab', 'ab'), 'a')\n",
  " assert_equal(solution.find_diff('abcd', 'abcde'), 'e')\n",
  " assert_equal(solution.find_diff('aaabbcdd', 'abdbacade'), 'e')\n",
+ " assert_equal(solution.find_diff_xor('ab', 'aab'), 'a')\n",
+ " assert_equal(solution.find_diff_xor('aab', 'ab'), 'a')\n",
+ " assert_equal(solution.find_diff_xor('abcd', 'abcde'), 'e')\n",
+ " assert_equal(solution.find_diff_xor('aaabbcdd', 'abdbacade'), 'e')\n",
  " print('Success: test_find_diff')\n",
  "\n",
  "\n",

arrays_strings/str_diff/str_diff_solution.ipynb

@@ -39,6 +39,7 @@
  " * The strings are lower case\n",
  "* Can we assume the inputs are valid?\n",
  " * No, check for None\n",
+ " * Otherwise, assume there is only a single different char between the two strings\n",
  "* Can we assume this fits memory?\n",
  " * Yes"
  ]
@@ -50,6 +51,8 @@
  "## Test Cases\n",
  "\n",
  "* None input -> TypeError\n",
+ "* 'ab', 'aab' -> 'a'\n",
+ "* 'aab', 'ab' -> 'a'\n",
  "* 'abcd', 'abcde' -> 'e'\n",
  "* 'aaabbcdd', 'abdbacade' -> 'e'"
  ]
@@ -65,6 +68,7 @@
  "* Keep a dictionary of seen values in s\n",
  "* Loop through t, decrementing the seen values\n",
  " * If the char is not there or if the decrement results in a negative value, return the char\n",
+ "* Return the differing char from the dictionary\n",
  "\n",
  "Complexity:\n",
  "* Time: O(m+n), where m and n are the lengths of s, t\n",
@@ -112,7 +116,8 @@
  " return char\n",
  " if seen[char] < 0:\n",
  " return char\n",
- " return None\n",
+ " for char, count in seen.items():\n",
+ " return char\n",
  "\n",
  " def find_diff_xor(self, str1, str2):\n",
  " if str1 is None or str2 is None:\n",
@@ -157,8 +162,14 @@
  " def test_find_diff(self):\n",
  " solution = Solution()\n",
  " assert_raises(TypeError, solution.find_diff, None)\n",
+ " assert_equal(solution.find_diff('ab', 'aab'), 'a')\n",
+ " assert_equal(solution.find_diff('aab', 'ab'), 'a')\n",
  " assert_equal(solution.find_diff('abcd', 'abcde'), 'e')\n",
  " assert_equal(solution.find_diff('aaabbcdd', 'abdbacade'), 'e')\n",
+ " assert_equal(solution.find_diff_xor('ab', 'aab'), 'a')\n",
+ " assert_equal(solution.find_diff_xor('aab', 'ab'), 'a')\n",
+ " assert_equal(solution.find_diff_xor('abcd', 'abcde'), 'e')\n",
+ " assert_equal(solution.find_diff_xor('aaabbcdd', 'abdbacade'), 'e')\n",
  " print('Success: test_find_diff')\n",
  "\n",
  "\n",

arrays_strings/str_diff/test_str_diff.py

@@ -6,8 +6,14 @@ class TestFindDiff(object):
  def test_find_diff(self):
  solution = Solution()
  assert_raises(TypeError, solution.find_diff, None)
+ assert_equal(solution.find_diff('ab', 'aab'), 'a')
+ assert_equal(solution.find_diff('aab', 'ab'), 'a')
  assert_equal(solution.find_diff('abcd', 'abcde'), 'e')
  assert_equal(solution.find_diff('aaabbcdd', 'abdbacade'), 'e')
+ assert_equal(solution.find_diff_xor('ab', 'aab'), 'a')
+ assert_equal(solution.find_diff_xor('aab', 'ab'), 'a')
+ assert_equal(solution.find_diff_xor('abcd', 'abcde'), 'e')
+ assert_equal(solution.find_diff_xor('aaabbcdd', 'abdbacade'), 'e')
  print('Success: test_find_diff')