[Python数据结构] 使用List实现Stack

[Python数据结构] 使用List实现Stack

1. Stack 
堆栈（Stack）又称为栈或堆叠，是计算机科学中一种特殊的串列形式的抽象数据类型（ADT），其特殊之处在于只能允许在阵列的一端进行加入数据和删除数据，并且执行顺序应按照后进先出（LIFO）的原则。
堆栈[维基百科]

2. Stack ADT
堆栈是一种抽象数据类型，其实例S需要支持两种方法：
　　1）S.push(e)  : add element e to the top of stack S
　　2）S.pop( )  : remove and return the top element from the stack S

另外，为了方便使用，我们还定义了以下方法：
　　3）S.top() : return the top element from the stack S, but not remove it
　　4）S.is_empty() : Return True if the stack is empty
　　5）len(S) : Return the number of elements in the stack

3. Implementing a Stack using a List

 class Empty(Exception):
     """Error attempting to access an element from an empty container"""
     pass

 class OverFlow(Exception):
     """Error attempting to push an element to an full container"""
     pass

 class ArrayStack():
     """LIFO Stack implementation using a Python list as underlying storage"""

     def __init__(self, n):
         """Create an empty stack."""
         self.data = []
         self.maxLen = n  # n : an integer that represent the max elements capacity of the stack

     def __len__(self):
         """Return the number of elements in the stack"""
         return len(self.data)

     def is_empty(self):
         """Return True if the stack is empty"""
         return len(self.data) == 0 

     def is_full(self):
         """Return True if the stack is full"""
         return len(self.data) == self.maxLen

     def push(self, e):
         """Add element e to the top of the stack

          Raise Empty exception if the stack is full"""
         if self.is_full():
             raise OverFlow('Stack is full')
         return self.data.append(e)

     def top(self):
         """Return the element at the top of the stack, but not move it.

         Raise Empty exception if the stack is empty"""
         if self.is_empty():
             raise Empty('Stack is empty')
         return self.data[-1]

     def pop(self):
         """Return the element at the top of the stack, meanwhile move it.

         Raise Empty exception if the stack is empty"""
         if self.is_empty():
             raise Empty('Stack is empty')
         return self.data.pop()

4. 执行结果：

 s = ArrayStack(10)
 l = np.random.randint(0, 10, size=(10, ))
 for i in l:
     s.push(i)

 s.data
 [6, 8, 7, 4, 2, 3, 4, 1, 5, 8]

 s.pop()
 8

 s.data
 [6, 8, 7, 4, 2, 3, 4, 1, 5]

 s.top()
 5

 s.data
 [6, 8, 7, 4, 2, 3, 4, 1, 5]