Fix doctests

Author: Hardvan

data_structures/linked_list/merge_sort_linked_list.py

@@ -5,14 +5,6 @@ class Node:
     Attributes:
         data (int): The data stored in the node.
         next (Node | None): A reference to the next node in the linked list.
-
-    >>> head = Node(4)
-    >>> head.next = Node(2)
-    >>> head.next.next = Node(1)
-    >>> head.next.next.next = Node(3)
-    >>> sorted_head = merge_sort_linked_list(head)
-    >>> print_linked_list(sorted_head)
-    1 2 3 4
     """
 
     def __init__(self, data: int) -> None:
@@ -22,39 +14,63 @@ def __init__(self, data: int) -> None:
 
 def get_middle(head: Node | None) -> Node | None:
     """
-    Find the middle node of the linked list using the slow and fast pointer technique.
+    Find the node before the middle of the linked list
+    using the slow and fast pointer technique.
 
     Parameters:
         head: The head node of the linked list.
 
     Returns:
-        The middle node of the linked list, or None if the list is empty.
+        The node before the middle of the linked list,
+        or None if the list has fewer than 2 nodes.
 
     Example:
     >>> head = Node(1)
     >>> head.next = Node(2)
     >>> head.next.next = Node(3)
     >>> middle = get_middle(head)
-    >>> middle.data if middle else None
+    >>> middle.data
     2
-    >>> get_middle(None) is None
-    True
     """
-
     if head is None or head.next is None:
-        return head
+        return None
+
+    slow: Node = head
+    fast: Node | None = head.next
 
-    slow: Node | None = head
-    fast: Node | None = head
     while fast is not None and fast.next is not None:
-        if slow is None:  # This should never happen, but it satisfies the type checker
-            return None
         slow = slow.next
         fast = fast.next.next
 
     return slow
 
 
+def print_linked_list(head: Node | None) -> None:
+    """
+    Print the linked list in a single line.
+
+    Parameters:
+        head: The head node of the linked list.
+
+    Example:
+    >>> head = Node(1)
+    >>> head.next = Node(2)
+    >>> head.next.next = Node(3)
+    >>> print_linked_list(head)
+    1 2 3
+    """
+
+    current = head
+    first = True  # To avoid printing space before the first element
+    while current:
+        if not first:
+            print(" ", end="")
+        print(current.data, end="")
+        first = False
+        current = current.next
+    print()
+
+
 def merge(left: Node | None, right: Node | None) -> Node | None:
     """
     Merge two sorted linked lists into one sorted linked list.
@@ -91,32 +107,6 @@ def merge(left: Node | None, right: Node | None) -> Node | None:
     return result
 
 
-def print_linked_list(head: Node | None) -> None:
-    """
-    Print the linked list in a single line.
-
-    Parameters:
-        head: The head node of the linked list.
-
-    Example:
-    >>> head = Node(1)
-    >>> head.next = Node(2)
-    >>> head.next.next = Node(3)
-    >>> print_linked_list(head)
-    1 2 3
-    """
-
-    current = head
-    first = True  # To avoid printing space before the first element
-    while current:
-        if not first:
-            print(" ", end="")
-        print(current.data, end="")
-        first = False
-        current = current.next
-    print()
-
-
 def merge_sort_linked_list(head: Node | None) -> Node | None:
     """
     Sort a linked list using the Merge Sort algorithm.
@@ -135,22 +125,6 @@ def merge_sort_linked_list(head: Node | None) -> Node | None:
     >>> sorted_head = merge_sort_linked_list(head)
     >>> print_linked_list(sorted_head)
     1 2 3 4
-
-    >>> head = Node(1)
-    >>> head.next = Node(2)
-    >>> head.next.next = Node(3)
-    >>> head.next.next.next = Node(4)
-    >>> sorted_head = merge_sort_linked_list(head)
-    >>> print_linked_list(sorted_head)
-    1 2 3 4
-
-    >>> head = Node(10)
-    >>> head.next = Node(3)
-    >>> head.next.next = Node(5)
-    >>> head.next.next.next = Node(1)
-    >>> sorted_head = merge_sort_linked_list(head)
-    >>> print_linked_list(sorted_head)
-    1 3 5 10
     """
 
     # Base Case: 0 or 1 node
@@ -159,17 +133,18 @@ def merge_sort_linked_list(head: Node | None) -> Node | None:
 
     # Split the linked list into two halves
     middle = get_middle(head)
-    if middle is None:
+    if middle is None or middle.next is None:
         return head
+
     next_to_middle = middle.next
     middle.next = None  # Split the list into two parts
 
-    left = merge_sort_linked_list(head)  # Sort left half
-    right = merge_sort_linked_list(next_to_middle)  # Sort right half
+    # Recursively sort both halves
+    left = merge_sort_linked_list(head)
+    right = merge_sort_linked_list(next_to_middle)
 
     # Merge sorted halves
-    sorted_list = merge(left, right)
-    return sorted_list
+    return merge(left, right)
 
 
 if __name__ == "__main__":