On the other hand, since simple associated lists by themselves do not let random access to the data or any form of efficient indexing, many basic operations — such as obtaining the last node of the list, finding a node that contains a given datum, or locating the place where a new node should be inserted — may necessitate iterate through most or all of the list components. They can be used to implement several other common abstract data types, including lists, stacks, queues, associative arrays, and S-expressions, though it is not uncommon to implement those data structures directly without use a associated list as the basis. The problem of machine translation for natural language processing led Victor Yngve at Massachusetts Institute of technology (MIT) to use associated lists as data structures in his COMIT programming language for computer research in the field of linguistics. Several operating systems developed by Technical system adviser (originally of West Lafayette Indiana, and later of Chapel Hill, North Carolina) used singly associated lists as file structures. The now-classic diagram consisting of blocks representing list nodes with arrows indicating to successive list nodes looks in" program the logic theory machine" by Newell and Shaw in Proc.
class Node: def __init__(self, data: int) -> int: self.data = data self.next = None class LinkedList: def __init__(self): self.head = None def push(self, new_data: int) -> int: new_node = Node(new_data) new_node.next = self.head self.head = new_node return self.head.data def middle_element(self) -> int: """ >>> link = LinkedList() >>> link.middle_element() No element found. >>> link.push(5) 5 >>> link.push(6) 6 >>> link.push(8) 8 >>> link.push(8) 8 >>> link.push(10) 10 >>> link.push(12) 12 >>> link.push(17) 17 >>> link.push(7) 7 >>> link.push(3) 3 >>> link.push(20) 20 >>> link.push(-20) -20 >>> link.middle_element() 12 >>> """ slow_pointer = self.head fast_pointer = self.head if self.head: while fast_pointer and fast_pointer.next: fast_pointer = fast_pointer.next.next slow_pointer = slow_pointer.next return slow_pointer.data else: print("No element found.") if __name__ == "__main__": link = LinkedList() for i in range(int(input().strip())): data = int(input().strip()) link.push(data) print(link.middle_element())