数据结构-栈

栈是链表的约束版本

新节点只能在栈顶插入和删除
后进先出的数据结构
最后一个节点设为None，表面是栈底
push和pop方法分别向栈添加和删除一个节点

实现分2个文件，测试采用1个文件

ListModule.py实现链表

# ListModule.py
# Classes List and Node definitions.

class Node:
   """Single node in a data structure"""

   def __init__( self, data ):
      """Node constructor"""
      
      self._data = data
      self._nextNode = None
    
   def __str__( self ):
      """Node data representation"""

      return str( self._data )      

class List:
   """Linked list"""

   def __init__( self ):
      """List constructor"""

      self._firstNode = None
      self._lastNode = None

   def __str__( self ):
      """List string representation"""

      if self.isEmpty():
         return "empty"

      currentNode = self._firstNode
      output = []

      while currentNode is not None:
         output.append( str( currentNode._data ) )
         currentNode = currentNode._nextNode

      return " ".join( output )      

   def insertAtFront( self, value ):
      """Insert node at front of list"""

      newNode = Node( value )

      if self.isEmpty():  # List is empty
         self._firstNode = self._lastNode = newNode
      else:   # List is not empty
         newNode._nextNode = self._firstNode
         self._firstNode = newNode
        
   def insertAtBack( self, value ):
      """Insert node at back of list"""

      newNode = Node( value )

      if self.isEmpty():  # List is empty
         self._firstNode = self._lastNode = newNode
      else:  # List is not empty
         self._lastNode._nextNode =  newNode
         self._lastNode = newNode

   def removeFromFront( self ):
      """Delete node from front of list"""

      if self.isEmpty():  # raise exception on empty list
         raise IndexError, "remove from empty list"

      tempNode = self._firstNode

      if self._firstNode is self._lastNode:  # one node in list
         self._firstNode = self._lastNode = None
      else:
         self._firstNode = self._firstNode._nextNode

      return tempNode

   def removeFromBack( self ):
      """Delete node from back of list"""

      if self.isEmpty():  # raise exception on empty list
         raise IndexError, "remove from empty list"
     
      tempNode = self._lastNode

      if self._firstNode is self._lastNode:  # one node in list
         self._firstNode = self._lastNode = None
      else:
         currentNode = self._firstNode

         # locate second-to-last node
         while currentNode._nextNode is not self._lastNode:
               currentNode = currentNode._nextNode
               
         currentNode._nextNode = None
         self._lastNode = currentNode

      return tempNode
    
   def isEmpty( self ):
      """Returns true if List is empty"""

      return self._firstNode is None

StackModule.py 为栈的实现

# StackModule.py
# Class Stack definition

from ListModule import List

class Stack( List ):
    """ Stack composed from linked list """

    def __init__( self ):
        """ Stack constructor """

        self._stackList = List()

    def __str__(self):
        """
         Stack string representation
        """

        return str( self._stackList )

    def push( self,element ):
        """
         push data onto stack
        """
        self._stackList.insertAtFront( element )

    def pop( self ):
        """
        pop data from stack
        """

        return self._stackList.removeFromFront()

    def isEmpty( self ):
        """
        Return 1 if Stack is empty
        """

        return self._stackList.isEmpty()

测试文件testStack.py

# testStack.py
# Driver to test class Stack

from StackModule import Stack

stack = Stack()

print "Processing a stack"

for i in range( 4 ):
    stack.push( i )
    print "The stack is ",stack

while not stack.isEmpty():
    pop = stack.pop()
    print pop,"popped from stack"
    print "The stack is: ", stack