220 lines
6.1 KiB
Python
220 lines
6.1 KiB
Python
######################################
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# DCS 229 -- Linked List
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# Linked List implementation
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# Date: 03/13/2026
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# Name: Benjamin Adovasio
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# Resources Used: https://docs.python.org/3/tutorial/datastructures.html
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##########################################
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from __future__ import annotations
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# https://docs.python.org/3/tutorial/errors.html#user-defined-exceptions
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# Want to define our own custom Exception class...
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class EmptyError(Exception):
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def __init__(self, message: str) -> None:
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super().__init__(message)
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self.message = message
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class Node[T]:
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''' class to implement a single node object in a singly-linked
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linked list '''
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def __init__(self, data: T):
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self.data = data
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self.next = None # points to another Node object
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def get_data(self) -> T:
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return self.data
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def set_data(self, value: T) -> None:
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self.data = value
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def get_next(self) -> Node[T]:
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return self.next
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def set_next(self, next_node: Node[T]) -> None:
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self.next = next_node
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class LinkedList[T]:
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''' class to implement a singly-linked linked list '''
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def __init__(self) -> None:
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self.head = None # the head pointer in the linked list
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self.size = 0
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def __len__(self) -> int:
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''' returns the number of nodes in the linked list
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Returns:
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int - representing the number of nodes in the list
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'''
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return self.size
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def insert_head(self, value: T) -> None:
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''' adds the given T-type data value to the front of the linked list
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Parameters:
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value: a type T data item to be included as the data in the inserted Node
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Returns:
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nothing
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'''
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## YOUR CODE HERE ##
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new_node = Node(value)
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new_node.set_next(self.head)
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self.head = new_node
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self.size += 1
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def insert_tail(self, value: T) -> None:
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''' adds the given T-type data value to the end of the linked list
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Parameters:
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value: a type T data item to be included as the data in the inserted Node
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Returns:
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nothing
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'''
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## YOUR CODE HERE ##
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new_node = Node(value)
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if self.head is None:
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self.head = new_node
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else:
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current = self.head
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while current.get_next() is not None:
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current = current.get_next()
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current.set_next(new_node)
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self.size += 1
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def remove_head(self) -> T:
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''' removes the first Node in the linked list, returning the data item
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inside that Node... Remember to handle the special case of an
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empty list (what should the head pointers be in that case?)
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and remember to update the head pointer when appropriate.
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Returns:
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a T type data item extracted from the removed Node
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Raises:
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EmptyError exception if list is empty
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'''
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# raise an error if list is empty
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# https://docs.python.org/3/tutorial/errors.html#user-defined-exceptions
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if self.size == 0:
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raise EmptyError("Cannot remove from an empy list")
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## YOUR CODE HERE ##
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removed_node = self.head
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self.head = self.head.get_next()
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self.size -= 1
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return removed_node.get_data()
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def remove_tail(self) -> T:
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''' removes the last Node in the linked list, returning the data item
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inside that Node... Remember to handle the special case of an
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empty list
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Returns:
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a T type data item extracted from the removed Node
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Raises:
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EmptyError exception if list is empty
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'''
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# raise an error if list is empty
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if self.size == 0:
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raise EmptyError("Cannot remove from an empy list")
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## YOUR CODE HERE ##
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if self.head.get_next() is None:
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removed_data = self.head.get_data()
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self.head = None
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self.size -= 1
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return removed_data
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current = self.head
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while current.get_next().get_next() is not None:
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current = current.get_next()
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removed_data = current.get_next().get_data()
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current.set_next(None)
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self.size -= 1
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return removed_data
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def __str__(self):
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''' returns a str representation of the linked list data
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Returns:
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an str representation of the linked list, showing head pointer
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and data tiems
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'''
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str_ = "head->"
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# start out at the head Node, and walk through Node by Node until we
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# reach the end of the linked list (i.e., the ._next entry is None)
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ptr_ = self.head
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while ptr_ is not None:
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str_ += "[" + str(ptr_.get_data()) + "]->"
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ptr_ = ptr_.get_next() # move ptr_ to the next Node in the linked list
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if self.head != None:
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str_ = str_[:-2] # remove trailing "->"
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str_ += "<-tail"
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return str_
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def main():
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# create a LinkedList and try out some various adds and removes
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ll = LinkedList()
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try:
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ll.remove_head()
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except EmptyError as err:
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print(err)
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ll.insert_head(8)
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assert len(ll) == 1
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removed = ll.remove_head()
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assert removed == 8
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assert len(ll) == 0
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ll.insert_tail(6)
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ll.insert_tail(7)
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ll.insert_tail(5)
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print(ll)
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assert len(ll) == 3
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removed = ll.remove_tail()
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assert removed == 5
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assert len(ll) == 2
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# ADD MORE TESTS
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# test inserting multiple at head
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ll.insert_head(1)
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ll.insert_head(2)
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ll.insert_head(3)
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assert len(ll) == 5
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print(ll)
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# test removing head repeatedly
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assert ll.remove_head() == 3
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assert ll.remove_head() == 2
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assert len(ll) == 3
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# test removing tail until empty
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assert ll.remove_tail() == 7
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assert ll.remove_tail() == 6
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assert ll.remove_tail() == 1
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assert len(ll) == 0
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# test removing from empty again
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try:
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ll.remove_tail()
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except EmptyError:
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print("Correctly caught empty list error")
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if __name__ == "__main__":
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main() |