Merge pull request #18 from miguelHx/master

Miguel solution to 1.2 - Check Permutation [Python]

Author: fvntr

Python/chapter01/1.2 - Check Perm/miguel_1.2_sol.py

@@ -0,0 +1,68 @@
+"""
+Python version 3.7.0
+1.2 - Check Permutation
+Given two strings, write a method to decide if one is a permutation of the other.
+"""
+import unittest
+import collections
+from typing import Callable
+
+
+def check_permutation(s1: str, s2: str) -> bool:
+    """
+    Determines if a s1 is a permutation of s2.
+    s1 is a permutation of s2 if the characters from s1 map to
+    the same characters in s2 in a one-to-one correspondence AND s1 and s2 are of the same length.
+    Runtime:  O(n + m), where n is the length of s1 and m is the length of s2.
+    Given:		            Expect:
+    "tacos", "costa"            True
+    "tacoos", "costa"           False
+    "swag", "hello"         False
+    "hi", "hello"           False
+    "hola", "loha"          True
+    "p3nding", "dingp3n"            True
+    "", "test"          False
+    "", ""          True
+    "test2", ""         False
+    :param s1: string of size n
+    :param s2: string of size m
+    :return: True if s1 is a permutation of s2, False otherwise
+    """
+    # precondition for a permutation, must be same length
+    if len(s1) != len(s2):
+        return False
+    # build histogram of seen characters in s1 and s2
+    # using histogram because string could have repeated characters
+    freqs_s1 = collections.Counter(s1)
+    freqs_s2 = collections.Counter(s2)
+    # compare frequencies of characters for s1 and s2
+    for key, val in freqs_s1.items():
+        if val != freqs_s2[key]:
+            # character counts between s1 and s2 don't match
+            return False
+    return True
+
+
+class TestCheckPermutationFunction(unittest.TestCase):
+    def _run_tests(self, f: Callable[[str, str], None]) -> None:
+        false_cases = [
+            ("tacoos", "costa"), ("swag", "hello"), ("hi", "hello"), ("tacooos", "costaaa"),
+            ("", "test"), ("test2", "")
+        ]
+        for case in false_cases:
+            self.assertFalse(f(case[0], case[1]), msg=case)
+
+        true_cases = [
+            ("tacos", "costa"), ("hola", "loha"), ("p3nding", "dingp3n"), ("same", "same"), ("", "")
+        ]
+        for case in true_cases:
+            self.assertTrue(f(case[0], case[1]), msg=case)
+        with self.assertRaises(TypeError):
+            f(8)
+
+    def test_check_permutation(self):
+        self._run_tests(check_permutation)
+
+
+if __name__ == '__main__':
+    unittest.main()