diff --git a/Chapter 1/2_Check Permutation/CheckPermutation.py b/Chapter 1/2_Check Permutation/CheckPermutation.py
deleted file mode 100644
index 811dbd8c..00000000
--- a/Chapter 1/2_Check Permutation/CheckPermutation.py	
+++ /dev/null
@@ -1,35 +0,0 @@
-# O(N)
-import unittest
-from collections import Counter
-
-def check_permutation(string):
-    str1 = string[0]
-    str2 = string[1]
-    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_string in self.dataT:
-            actual = check_permutation(test_string)
-            self.assertTrue(actual)
-        # false check
-        for test_string in self.dataF:
-            actual = check_permutation(test_string)
-            self.assertFalse(actual)
-
-if __name__ == "__main__":
-    unittest.main()
diff --git a/Chapter 1/1_Is Unique/IsUnique.py b/Chapter1/1_Is Unique/IsUnique.py
similarity index 100%
rename from Chapter 1/1_Is Unique/IsUnique.py
rename to Chapter1/1_Is Unique/IsUnique.py
diff --git a/Chapter1/2_Check Permutation/CheckPermutation.py b/Chapter1/2_Check Permutation/CheckPermutation.py
new file mode 100644
index 00000000..49046309
--- /dev/null
+++ b/Chapter1/2_Check Permutation/CheckPermutation.py	
@@ -0,0 +1,43 @@
+# 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()
diff --git a/Chapter 1/3_URLify/URLify.py b/Chapter1/3_URLify/URLify.py
similarity index 100%
rename from Chapter 1/3_URLify/URLify.py
rename to Chapter1/3_URLify/URLify.py
diff --git a/Chapter 1/4_Palindrome Permutation/PalindromePermutation.py b/Chapter1/4_Palindrome Permutation/PalindromePermutation.py
similarity index 100%
rename from Chapter 1/4_Palindrome Permutation/PalindromePermutation.py
rename to Chapter1/4_Palindrome Permutation/PalindromePermutation.py
diff --git a/Chapter 1/5_One Away/OneAway.py b/Chapter1/5_One Away/OneAway.py
similarity index 100%
rename from Chapter 1/5_One Away/OneAway.py
rename to Chapter1/5_One Away/OneAway.py
diff --git a/Chapter 1/6_String Compression/StringCompression.py b/Chapter1/6_String Compression/StringCompression.py
similarity index 100%
rename from Chapter 1/6_String Compression/StringCompression.py
rename to Chapter1/6_String Compression/StringCompression.py
diff --git a/Chapter 1/7_Rotate Matrix/RotateMatrix.py b/Chapter1/7_Rotate Matrix/RotateMatrix.py
similarity index 100%
rename from Chapter 1/7_Rotate Matrix/RotateMatrix.py
rename to Chapter1/7_Rotate Matrix/RotateMatrix.py
diff --git a/Chapter 1/8_Zero Matrix/ZeroMatrix.py b/Chapter1/8_Zero Matrix/ZeroMatrix.py
similarity index 100%
rename from Chapter 1/8_Zero Matrix/ZeroMatrix.py
rename to Chapter1/8_Zero Matrix/ZeroMatrix.py
diff --git a/Chapter 1/9_String Rotation/StringRotation.py b/Chapter1/9_String Rotation/StringRotation.py
similarity index 100%
rename from Chapter 1/9_String Rotation/StringRotation.py
rename to Chapter1/9_String Rotation/StringRotation.py
diff --git a/Chapter 2/1_Remove_Dups.py b/Chapter2/1_Remove_Dups.py
similarity index 100%
rename from Chapter 2/1_Remove_Dups.py
rename to Chapter2/1_Remove_Dups.py
diff --git a/Chapter 2/2_Return_Kth_To_Last.py b/Chapter2/2_Return_Kth_To_Last.py
similarity index 100%
rename from Chapter 2/2_Return_Kth_To_Last.py
rename to Chapter2/2_Return_Kth_To_Last.py
diff --git a/Chapter 2/3_Delete_Middle_Node.py b/Chapter2/3_Delete_Middle_Node.py
similarity index 100%
rename from Chapter 2/3_Delete_Middle_Node.py
rename to Chapter2/3_Delete_Middle_Node.py
diff --git a/Chapter 2/4_Partition.py b/Chapter2/4_Partition.py
similarity index 100%
rename from Chapter 2/4_Partition.py
rename to Chapter2/4_Partition.py
diff --git a/Chapter 2/5_Sum_Lists.py b/Chapter2/5_Sum_Lists.py
similarity index 100%
rename from Chapter 2/5_Sum_Lists.py
rename to Chapter2/5_Sum_Lists.py
diff --git a/Chapter 2/6_Palindrome.py b/Chapter2/6_Palindrome.py
similarity index 100%
rename from Chapter 2/6_Palindrome.py
rename to Chapter2/6_Palindrome.py
diff --git a/Chapter 2/7_Intersection.py b/Chapter2/7_Intersection.py
similarity index 100%
rename from Chapter 2/7_Intersection.py
rename to Chapter2/7_Intersection.py
diff --git a/Chapter 2/8_Loop_Detection.py b/Chapter2/8_Loop_Detection.py
similarity index 100%
rename from Chapter 2/8_Loop_Detection.py
rename to Chapter2/8_Loop_Detection.py
diff --git a/Chapter 2/LinkedList.py b/Chapter2/LinkedList.py
similarity index 100%
rename from Chapter 2/LinkedList.py
rename to Chapter2/LinkedList.py
diff --git a/Chapter4/README.md b/Chapter4/README.md
new file mode 100644
index 00000000..e69539d3
--- /dev/null
+++ b/Chapter4/README.md
@@ -0,0 +1 @@
+# Trees and graphs
diff --git a/README.md b/README.md
new file mode 100644
index 00000000..8ba92013
--- /dev/null
+++ b/README.md
@@ -0,0 +1,9 @@
+# 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.
diff --git a/readme.md b/readme.md
deleted file mode 100644
index 7f913ae8..00000000
--- a/readme.md
+++ /dev/null
@@ -1,5 +0,0 @@
-##Python Solutions to Cracking the Coding Interview 6th Edition
-
-To run the programs, just use the `python filename.py` command.
-
-The test cases are included in the solution files.
\ No newline at end of file