148 exam practice

practice.py

class BTNode:
    def __init__(self, value=None, left=None, right=None):
        self.value, self.left, self.right = value, left, right


def count_leaves(root: 'BTNode') -> int:
    """ Return the number of leaves in the tree rooted at root.
    >>> count_leaves(None)
    0
    >>> count_leaves(BTNode(0, None, None))
    1
    >>> count_leaves(BTNode(0, BTNode(1, BTNode(BTNode(3), BTNode(4))), BTNode(2)))
    """

    if not root:
        return 0
    
    if not root.left and not root.right:
        return 1

    count = 0

    if root.left:
        count += count_leaves(root.left)

    if root.right:
        count += count_leaves(root.right)

    return count


class Node:
    """Node in a linked list"""

    def __init__(self: 'Node', value: object, next: 'Node' = None) -> None:
        """Create Node self with data value and successor next."""
        self.value, self.next = value, next


class LinkedList:
    """Collection of Nodes to form a linked list"""

    def __init__(self: 'LinkedList') -> None:
        """Create empty LinkedList"""
        self.front, self.back, self.size = None, None, 0

    def remove_last(self: 'LinkedList') -> None:
        """ Remove last node of self.
        >>> lst = LinkedList()
        >>> back = Node(3)
        >>> lst.front = Node(2, Node(5, Node(7, back)))
        >>> lst.back = back
        >>> lst.remove_last()
        >>> lst.remove_last()
        >>> lst.back.value
        5
        """
        current = self.front
        while current.next is not self.back:
            current = current.next
        self.back = current