Merge pull request YearOfProgramming#102 from ningyuansg/master

[Python] Challenges #0, YearOfProgramming#1, YearOfProgramming#2, YearOfProgramming#3, YearOfProgramming#4

challenge_0/python/ning/challenge_0.py

@@ -0,0 +1 @@
+print('Hello World!')

challenge_1/python/ning/challenge_1.py

@@ -0,0 +1,6 @@
+def reverse_string(original_string):
+    return original_string[::-1]
+
+original_string = str(input("Enter a string to be reversed > "))
+print(reverse_string(original_string))
+

challenge_2/python/ning/challenge_2.py

@@ -0,0 +1,19 @@
+from collections import defaultdict
+
+def find_unique(sequence):
+    counter_dict = defaultdict(int)
+    uniques = []
+
+    for item in sequence:
+        counter_dict[item] += 1
+
+    for item, count in counter_dict.items():
+        if count == 1:
+            uniques.append(item)
+
+    return uniques
+
+test_sequence_list = [2,'a','l',3,'l',4,'k',2,3,4,'a',6,'c',4,'m',6,'m','k',9,10,9,8,7,8,10,7]
+
+print(find_unique(test_sequence_list))
+

challenge_3/python/ning/challenge_3.py

@@ -0,0 +1,4 @@
+from collections import Counter
+
+test_sequence_list = [2,2,3,7,5,7,7,7,4,7,2,7,4,5,6,7,7,8,6,7,7,8,10,12,29,30,19,10,7,7,7,7,7,7,7,7,7]
+print(Counter(test_sequence_list).most_common(1)[0][0])

challenge_4/python/ning/challenge_4.py

@@ -0,0 +1,30 @@
+class BTree:
+    def __init__(self, b_tree_list=list()):
+        self.b_tree_list = b_tree_list
+        self.levels = len(b_tree_list)
+
+    def visualise(self):
+        for index, level in enumerate(self.b_tree_list):
+            spacing = 2 ** (self.levels - index) - 1
+            print(((spacing-1)//2)*' ', end='')
+            for node in level:
+                if node is None:
+                    print(' ', end='')
+                else:
+                    print(node, end='')
+                print(spacing * ' ', end='')
+            print('')  # newline
+
+    def invert(self):
+        for level in self.b_tree_list:
+            level.reverse()
+
+
+example_tree = BTree([
+    [4],
+    [2, 7],
+    [1, 3, 6, 9]])
+
+example_tree.visualise()
+example_tree.invert()
+example_tree.visualise()