add merge sort

Author: Michael

src/merge_sort.py

@@ -0,0 +1,65 @@
+import unittest
+from typing import List
+import random
+
+
+def merge_sort(inp: List[int]):
+    """
+    split the input (n elements) into 2 sub-arrays with n/2 elements
+    sort these 2 sub-arrays recursively by merge_sort
+    merge 2 sorted sub-arrays to produce the result
+    :param inp:
+    :return:
+    """
+    if len(inp) <= 1:
+        return inp
+    # split
+    mid_index = len(inp) // 2
+    # sort sub-lists
+    left = inp[:mid_index]
+    right = inp[mid_index:]
+    print(f'left: {left}, right: {right}')
+    left = merge_sort(inp[:mid_index])
+    right = merge_sort(inp[mid_index:])
+
+    # merge sorted sub-lists
+    left_index = 0
+    right_index = 0
+    i = 0
+    while i < len(inp):
+        if left[left_index] >= right[right_index]:
+            inp[i] = right[right_index]
+            right_index += 1
+        else:
+            inp[i] = left[left_index]
+            left_index += 1
+        i += 1
+        if left_index == len(left):
+            inp[i:] = right[right_index:]
+            break
+        if right_index == len(right):
+            inp[i:] = left[left_index:]
+            break
+    return inp
+
+
+class MergeSortTest(unittest.TestCase):
+
+    def test_case1(self):
+        input = [1, 2, 3, 4, 5]
+        self.assertEqual(input, merge_sort(input))
+
+    def test_case2(self):
+        input = [5, 4, 3, 2, 1]
+        self.assertEqual([1, 2, 3, 4, 5], merge_sort(input))
+
+    def test_cases(self):
+        random.seed(42)
+        for i in range(0, 50):
+            inp = random.sample(range(0, 10), 10)
+            print(f'input: {inp}')
+            self.assertEqual([0,1,2,3,4,5,6,7,8,9], merge_sort(inp))
+
+
+if __name__ == '__main__':
+    unittest.main()