Add function to remove nth node from end of linked list

Introduce `remove_nth_from_end` function to handle linked list node removal by position from the end. Includes helper function for list length calculation and a test case to verify correctness.

Author: nicholasadamou

Linked Lists/remove_node_from_end_of_linked_list.py

@@ -0,0 +1,66 @@
+# https://neetcode.io/problems/remove-node-from-end-of-linked-list
+
+from typing import Optional
+
+import unittest
+
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+def remove_nth_from_end(head: Optional[ListNode], n: int) -> Optional[ListNode]:
+    def get_length(head: Optional[ListNode]):
+        length: int = 0
+
+        current: ListNode = head
+
+        while current:
+            length += 1
+
+            current = current.next
+
+        return length
+
+    length: int = get_length(head)
+
+    # When the node to remove is the `head` itself
+    if length == n:
+        return head.next
+
+    target_index: int = length - n
+
+    current: ListNode = head
+    previous: ListNode = ListNode()
+    count: int = 0
+
+    while current:
+        if count == target_index:
+            previous.next = current.next
+            break
+
+        previous = current
+        current = current.next
+
+        count += 1
+
+    return head
+
+class Test(unittest.TestCase):
+    def test_example(self):
+        # Create the linked list 1 -> 2 -> 3 -> 4 -> 5
+        head = ListNode(1)
+        head.next = ListNode(2)
+        head.next.next = ListNode(3)
+        head.next.next.next = ListNode(4)
+        head.next.next.next.next = ListNode(5)
+
+        # Remove the 2nd node from the end, which is '4'
+        new_head = remove_nth_from_end(head, 2)
+
+        # Verify the new linked list is 1 -> 2 -> 3 -> 5
+        self.assertEqual(new_head.val, 1)
+        self.assertEqual(new_head.next.val, 2)
+        self.assertEqual(new_head.next.next.val, 3)
+        self.assertEqual(new_head.next.next.next.val, 5)
+        self.assertIsNone(new_head.next.next.next.next)