Python实现栈（基于数组和单链表两种）

前言

使用Python 实现栈。
两种实现方式：

• 基于数组 - 数组同时基于链表实现
• 基于单链表 - 单链表的节点时一个实例化的node 对象

完整代码可见GitHub：
https://github.com/GYT0313/Python-DataStructure/tree/master/5-stack

目录结构：

注：一个完整的代码并不是使用一个py文件，而使用了多个文件通过继承方式实现。

1. 超类接口代码

arraycollection.py

"""
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

abstractstack.py

"""
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)

2. 基于数组

运行示例：

代码：
栈实现：arraystack.py

"""
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)

数组实现：arrays.py

"""
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

3. 基于链表

运行示例：

代码：
linkedstack.py

"""
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.")

node.py

"""
链表结构的节点类
"""

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

参考：《数据结构（Python语言描述）》

完！

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