Merge pull request #720 from nanto88/master

add example of merge sort in python

Author: probot-auto-merge[bot]

Python/MergeSort.py

@@ -0,0 +1,56 @@
+# -*- coding: utf-8 -*-
+def merge(left_list, right_list):
+    sorted_list = []
+    left_list_index = right_list_index = 0
+
+    # We use the list lengths often, so its handy to make variables
+    left_list_length, right_list_length = len(left_list), len(right_list)
+
+    for _ in range(left_list_length + right_list_length):
+        if left_list_index < left_list_length and right_list_index < right_list_length:
+            # We check which value from the start of each list is smaller
+            # If the item at the beginning of the left list is smaller, add it
+            # to the sorted list
+            if left_list[left_list_index] <= right_list[right_list_index]:
+                sorted_list.append(left_list[left_list_index])
+                left_list_index += 1
+            # If the item at the beginning of the right list is smaller, add it
+            # to the sorted list
+            else:
+                sorted_list.append(right_list[right_list_index])
+                right_list_index += 1
+
+        # If we've reached the end of the of the left list, add the elements
+        # from the right list
+        elif left_list_index == left_list_length:
+            sorted_list.append(right_list[right_list_index])
+            right_list_index += 1
+        # If we've reached the end of the of the right list, add the elements
+        # from the left list
+        elif right_list_index == right_list_length:
+            sorted_list.append(left_list[left_list_index])
+            left_list_index += 1
+
+    return sorted_list
+
+
+def merge_sort(nums):
+    # If the list is a single element, return it
+    if len(nums) <= 1:
+        return nums
+
+    # Use floor division to get midpoint, indices must be integers
+    mid = len(nums) // 2
+
+    # Sort and merge each half
+    left_list = merge_sort(nums[:mid])
+    right_list = merge_sort(nums[mid:])
+
+    # Merge the sorted lists into a new one
+    return merge(left_list, right_list)
+
+# time complexity : O(nlog(n))
+if __name__ == '__main__':
+    nums = [210, 24, 60, 300, 180]
+    sorted_nums = merge_sort(nums)
+    print(sorted_nums)