[+] A1 Starter Files

assignments/A1/a1_linked_list.py

@@ -0,0 +1,169 @@
+"""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