Fixed linked list bug (#2481)

* * fixed __getitem__() function
* add test

* * updated doctests
* updated __setitem__() func

* fixup! Format Python code with psf/black push

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

Author: realDuYuanChao

Diff for: backtracking/minimax.py

@@ -1,4 +1,5 @@
 from __future__ import annotations
+
 import math
 
 """ Minimax helps to achieve maximum score in a game by checking all possible moves
@@ -10,8 +11,9 @@
 """
 
 
-def minimax(depth: int, node_index: int, is_max: bool,
-            scores: list[int], height: float) -> int:
+def minimax(
+    depth: int, node_index: int, is_max: bool, scores: list[int], height: float
+) -> int:
     """
     >>> import math
     >>> scores = [90, 23, 6, 33, 21, 65, 123, 34423]

Diff for: data_structures/linked_list/singly_linked_list.py

@@ -47,22 +47,51 @@ def __repr__(self):
     def __getitem__(self, index):
         """
         Indexing Support. Used to get a node at particular position
+        >>> linked_list = LinkedList()
+        >>> for i in range(0, 10):
+        ...     linked_list.insert_nth(i, i)
+        >>> all(str(linked_list[i]) == str(i) for i in range(0, 10))
+        True
+        >>> linked_list[-10]
+        Traceback (most recent call last):
+        ...
+        ValueError: list index out of range.
+        >>> linked_list[len(linked_list)]
+        Traceback (most recent call last):
+        ...
+        ValueError: list index out of range.
         """
-        if index < 0:
-            raise ValueError("Negative indexes are not yet supported")
+        if not 0 <= index < len(self):
+            raise ValueError("list index out of range.")
         for i, node in enumerate(self):
             if i == index:
-                return node.data
+                return node
 
     # Used to change the data of a particular node
     def __setitem__(self, index, data):
+        """
+        >>> linked_list = LinkedList()
+        >>> for i in range(0, 10):
+        ...     linked_list.insert_nth(i, i)
+        >>> linked_list[0] = 666
+        >>> linked_list[0]
+        666
+        >>> linked_list[5] = -666
+        >>> linked_list[5]
+        -666
+        >>> linked_list[-10] = 666
+        Traceback (most recent call last):
+        ...
+        ValueError: list index out of range.
+        >>> linked_list[len(linked_list)] = 666
+        Traceback (most recent call last):
+        ...
+        ValueError: list index out of range.
+        """
+        if not 0 <= index < len(self):
+            raise ValueError("list index out of range.")
         current = self.head
-        # If list is empty
-        if current is None:
-            raise IndexError("The Linked List is empty")
         for i in range(index):
-            if current.next is None:
-                raise IndexError("list index out of range")
             current = current.next
         current.data = data
 
@@ -163,8 +192,15 @@ def test_singly_linked_list() -> None:
     assert linked_list.delete_head() == 0
     assert linked_list.delete_nth(9) == 10
     assert linked_list.delete_tail() == 11
+    assert len(linked_list) == 9
     assert str(linked_list) == "->".join(str(i) for i in range(1, 10))
 
+    assert all(linked_list[i] == i + 1 for i in range(0, 9)) is True
+
+    for i in range(0, 9):
+        linked_list[i] = -i
+    assert all(linked_list[i] == -i for i in range(0, 9)) is True
+
 
 def main():
     from doctest import testmod