"""
File: abstractcollection.py
Author: Ken Lambert
"""

class AbstractCollection(object):
  """An abstract collection implementation."""

  # Constructor
  def __init__(self, sourceCollection = None):
    """Sets the initial state of self, which includes the
    contents of sourceCollection, if it's present."""
    self._size = 0
    if sourceCollection:
      for item in sourceCollection:
        self.add(item)

  # Accessor methods
  def isEmpty(self):
    """Returns True if len(self) == 0, or False otherwise."""
    return len(self) == 0
  
  def __len__(self):
    """Returns the number of items in self."""
    return self._size

  def __str__(self):
    """Returns the string representation of self."""
    return "[" + ", ".join(map(str, self)) + "]"

  def __add__(self, other):
    """Returns a new bag containing the contents
    of self and other."""
    result = type(self)(self)
    for item in other:
      result.add(item)
    return result

  def __eq__(self, other):
    """Returns True if self equals other,
    or False otherwise."""
    if self is other: return True
    if type(self) != type(other) or       len(self) != len(other):
      return False
    otherIter = iter(other)
    for item in self:
      if item != next(otherIter):
        return False
    return True

"""
File: abstractstack.py
Author: Ken Lambert
"""

from abstractcollection import AbstractCollection

class AbstractStack(AbstractCollection):
  """An abstract stack implementation."""

  # Constructor
  def __init__(self, sourceCollection = None):
    """Sets the initial state of self, which includes the
    contents of sourceCollection, if it's present."""
    AbstractCollection.__init__(self, sourceCollection)

  # Mutator methods
  def add(self, item):
    """Adds item to self."""
    self.push(item)

"""
File: abstractstack.py
Author: Ken Lambert
"""

from abstractcollection import AbstractCollection

class AbstractStack(AbstractCollection):
  """An abstract stack implementation."""

  # Constructor
  def __init__(self, sourceCollection = None):
    """Sets the initial state of self, which includes the
    contents of sourceCollection, if it's present."""
    AbstractCollection.__init__(self, sourceCollection)

  # Mutator methods
  def add(self, item):
    """Adds item to self."""
    self.push(item)

"""
File: arrays.py

An Array is a restricted list whose clients can use
only [], len, iter, and str.

To instantiate, use

<variable> = array(<capacity>, <optional fill value>)

The fill value is None by default.
"""

class Array(object):
  """Represents an array."""

  def __init__(self, capacity, fillValue = None):
    """Capacity is the static size of the array.
    fillValue is placed at each position."""
    self._items = list()
    for count in range(capacity):
      self._items.append(fillValue)

  def __len__(self):
    """-> The capacity of the array."""
    return len(self._items)

  def __str__(self):
    """-> The string representation of the array."""
    return str(self._items)

  def __iter__(self):
    """Supports iteration over a view of an array."""
    return iter(self._items)

  def __getitem__(self, index):
    """Subscript operator for access at index."""
    return self._items[index]

  def __setitem__(self, index, newItem):
    """Subscript operator for replacement at index."""
    self._items[index] = newItem

"""
linkedstack.py
"""

from node import Node
from abstractstack import AbstractStack

class LinkedStack(AbstractStack):
  """基于单链表实现栈-链表头部为栈顶"""

  def __init__(self, source_collection=None):
    self._items = None
    AbstractStack.__init__(self, source_collection)

  def __iter__(self):
    """迭代-使用一个列表实现, 列表第一项为单链表的最后一项"""
    def visit_nodes(node):
      if node != None:
        visit_nodes(node.next)
        temp_list.append(node.data)
    temp_list = []
    visit_nodes(self._items)
    return iter(temp_list)

  def peek(self):
    """返回栈顶元素"""
    self._prior_condition()
    return self._items.data

  def clear(self):
    """清空列表"""
    self._size = 0
    self._items = None

  def push(self, item):
    """入栈"""
    self._items = Node(item, self._items)
    self._size += 1

  def pop(self):
    """出栈"""
    self._prior_condition()
    old_item = self._items.data
    self._items = self._items.next
    self._size -= 1
    return old_item

  def _prior_condition(self):
    if self._size == 0:
      raise KeyError("The stack is empty.")

"""
链表结构的节点类
"""

class Node(object):
  def __init__(self, data, next=None):
    self.data = data
    self.next = next