Optimize file CheckPermutation.py to be more Pythonic.

Chapter1/2_Check Permutation/CheckPermutation.py

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+# O(N)
+import unittest
+from collections import Counter
+
+
+def check_permutation(str1, str2):
+    if len(str1) != len(str2):
+        return False
+    counter = Counter()
+    for c in str1:
+        counter[c] += 1
+    for c in str2:
+        if counter[c] == 0:
+            return False
+        counter[c] -= 1
+    return True
+
+
+class Test(unittest.TestCase):
+    dataT = (
+        ('abcd', 'bacd'),
+        ('3563476', '7334566'),
+        ('wef34f', 'wffe34'),
+    )
+    dataF = (
+        ('abcd', 'd2cba'),
+        ('2354', '1234'),
+        ('dcw4f', 'dcw5f'),
+    )
+
+    def test_cp(self):
+        # true check
+        for test_strings in self.dataT:
+            result = check_permutation(*test_strings)
+            self.assertTrue(result)
+        # false check
+        for test_strings in self.dataF:
+            result = check_permutation(*test_strings)
+            self.assertFalse(result)
+
+
+if __name__ == "__main__":
+    unittest.main()

Chapter4/README.md

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+# Trees and graphs

README.md

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+# Python Solutions to *Cracking the Coding Interview, 6th Edition*
+
+This is a **Python** solutions for the book [Cracking the Coding Interview, 6th Edition](https://www.careercup.com/book) by *Gayle Laakmann McDowell*.
+
+## How to use?
+
+To run the programs, just use the `python ChapterX/filename.py` command.
+
+The test cases are included in the solution files.