TheAlgorithms · aryandgandhi · Oct 5, 2023 · Oct 5, 2023 · Oct 5, 2023 · Oct 5, 2023
diff --git a/data_structures/linked_list/remove_nth_node_from_end_of_list.py b/data_structures/linked_list/remove_nth_node_from_end_of_list.py
@@ -0,0 +1,143 @@
+"""Learn more about this algorithm: https://www.geeksforgeeks.org/delete-nth-node-from-the-end-of-the-given-linked-list/"""
+
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Node:
+    def __init__(self, data: int) -> None:
+        self.data = data
+        self.next: Node | None = None
+
+
+class LinkedListExceptionError(Exception):
+    pass
+
+
+class LinkedList:
+    def __init__(self) -> None:
+        self.head: Node | None = None
+
+    # pulled from middle_element_of_linked_list
+    def append(self, new_data: int) -> int:
+        """
+        >>> link = LinkedList()
+        >>> link.append(5)
+        5
+        >>> link.append(6)
+        6
+        """
+        new_node = Node(new_data)
+        new_node.next = self.head
+        self.head = new_node
+        if not self.head:
+            raise LinkedListExceptionError(
+                "Unexpected error: Head of linked list is None after append operation."
+            )
+        return self.head.data
+
+    def view(self) -> str:
+        """
+        >>> link = LinkedList()
+        >>> link.append(5)
+        5
+        >>> link.append(6)
+        6
+        >>> link.view()
+        '6->5'
+        """
+        ret = ""
+        temp = self.head
+        while temp is not None:
+            ret += str(temp.data)
+            ret += "->"
+            temp = temp.next
+        return ret[:-2]
+
+    def remove_nth_from_end(self, position_from_end: int) -> Node | None:
+        """
+        >>> link = LinkedList()
+        >>> link.remove_nth_from_end(3)
+        Traceback (most recent call last):
+        ...
+        IndexError: No element found.
+        >>> link.append(5)
+        5
+        >>> link.append(6)
+        6
+        >>> link.append(8)
+        8
+        >>> link.append(8)
+        8
+        >>> link.append(10)
+        10
+        >>> link.append(12)
+        12
+        >>> link.append(17)
+        17
+        >>> link.remove_nth_from_end(100)
+        Traceback (most recent call last):
+        ...
+        IndexError: Index out of bounds error.
+        >>> link.append(-25)
+        -25
+        >>> link.append(-20)
+        -20
+        >>> link.remove_nth_from_end(3)
+        Node()
+        >>>
+        """
+        # want to have two pointers, one at the start and the other k nodes forward
+        # We could complete this in one pass if we stored a self.size variable
+        if not self.head:
+            raise IndexError("No element found.")
+
+        size = 0
+        current: Node | None = self.head
+        while current:
+            size += 1
+            current = current.next
+
+        if position_from_end > size or position_from_end <= 0:
+            raise IndexError("Index out of bounds error.")
+            return None
+
+        first: Node | None = self.head
+        for _i in range(position_from_end):
+            if first:
+                first = first.next
+
+        # This condition checks if position_from_end is equal to the size of the list.
+        # If it is, then we simply delete the head node of the list.
+        if not first:
+            self.head = self.head.next if self.head else None
+            return self.head
+
+        second: Node | None = self.head
+        prev: Node | None = None
+
+        while first:
+            first = first.next
+            prev = second
+            if second:
+                second = second.next
+
+        if prev and second:
+            prev.next = second.next
+
+        return self.head
+
+
+if __name__ == "__main__":
+    link = LinkedList()
+    for _ in range(int(input().strip())):
+        data = int(input().strip())
+        link.append(data)
+    print("Before list: ")
+    print(link.view())
+    print(link.remove_nth_from_end(int(input().strip())))
+    print("After list: ")
+    print(link.view())