CSC111/assignments/A1/a1_linked_list.py

"""CSC111 Winter 2021 Assignment 1: Linked Lists

Do not change this file -- it will not be submitted, and we will supply our own copy
for grading purposes.

Copyright and Usage Information
===============================

This file is provided solely for the personal and private use of students
taking CSC111 at the University of Toronto St. George campus. All forms of
distribution of this code, whether as given or with any changes, are
expressly prohibited. For more information on copyright for CSC111 materials,
please consult our Course Syllabus.

This file is Copyright (c) 2021 David Liu and Isaac Waller.
"""
from __future__ import annotations
from dataclasses import dataclass
from typing import Any, Iterable, Optional


@dataclass
class _Node:
    """A node in a linked list.

    Note that this is considered a "private class", one which is only meant
    to be used in this module by the LinkedList class, but not by client code.

    Instance Attributes:
      - item: The data stored in this node.
      - next: The next node in the list, if any.
    """
    item: Any
    next: Optional[_Node] = None  # By default, this node does not link to any other node


class LinkedList:
    """A linked list implementation of the List ADT.
    """
    # Private Instance Attributes:
    #   - _first: The first node in the linked list, or None if the list is empty.
    _first: Optional[_Node]

    def __init__(self, items: Iterable) -> None:
        """Initialize a new linked list containing the given items.
        """
        self._first = None
        for item in items:
            self.append(item)

    def to_list(self) -> list:
        """Return a built-in Python list containing the items of this linked list.

        The items in this linked list appear in the same order in the returned list.
        """
        items_so_far = []

        curr = self._first
        while curr is not None:
            items_so_far.append(curr.item)
            curr = curr.next

        return items_so_far

    def __len__(self) -> int:
        """Return the number of elements in this list.

        >>> lst = LinkedList([])
        >>> len(lst)              # Equivalent to lst.__len__()
        0
        >>> lst = LinkedList([1, 2, 3])
        >>> len(lst)
        3
        """
        curr = self._first
        len_so_far = 0
        while curr is not None:
            len_so_far += 1
            curr = curr.next

        return len_so_far

    def __contains__(self, item: Any) -> bool:
        """Return whether item is in this linked list.
        """
        curr = self._first
        while curr is not None:
            if curr.item == item:
                return True

            curr = curr.next
        return False

    def __getitem__(self, i: int) -> Any:
        """Return the item stored at index i in this linked list.

        Raise an IndexError if index i is out of bounds.

        Preconditions:
            - i >= 0
        """
        curr = self._first
        curr_index = 0

        while curr is not None:
            if curr_index == i:
                return curr.item

            curr = curr.next
            curr_index = curr_index + 1

        # If we've reached the end of the list and no item has been returned,
        # the given index is out of bounds.
        raise IndexError

    def pop(self, i: int) -> Any:
        """Remove and return the item at index i.

        Raise IndexError if i >= len(self).

        Preconditions:
            - i >= 0

        >>> lst = LinkedList([1, 2, 10, 200])
        >>> lst.pop(1)
        2
        >>> lst.to_list()
        [1, 10, 200]
        """
        if i == 0:
            if self._first is None:
                raise IndexError
            else:
                item = self._first.item
                self._first = self._first.next
                return item
        else:
            curr = self._first
            curr_index = 0

            while not (curr is None or curr_index == i - 1):
                curr = curr.next
                curr_index = curr_index + 1

            if curr is None:
                raise IndexError
            else:
                if curr.next is None:
                    raise IndexError
                else:
                    item = curr.next.item
                    curr.next = curr.next.next
                    return item

    def append(self, item: Any) -> None:
        """Add the given item to the end of this linked list.
        """
        new_node = _Node(item)

        if self._first is None:
            self._first = new_node
        else:
            curr = self._first
            while curr.next is not None:
                curr = curr.next

            # After the loop, curr is the last node in the LinkedList.
            assert curr is not None and curr.next is None
            curr.next = new_node