数据结构：栈 顺序表方法和单链表方法（python版）

#!/usr/bin/env python
# -*- coding:utf-8 -*-


class StackUnderflow(ValueError):
    pass

#链表节点
class Node(object):
    def __init__(self, elem, next_ = None):
        self.elem = elem
        self.next = next_

#顺序表实现栈
class SStack(object):
    def __init__(self):
        self._elems = []

    def is_empty(self):
        return self._elems == []

    def top(self):
        if self.is_empty():
            raise StackUnderflow
        return self._elems[-1]

    def push(self, elem):
        self._elems.append(elem)

    def pop(self):
        if self.is_empty():
            raise StackUnderflow
        return self._elems.pop()

#链表实现栈
class LStack(object):
    def __init__(self):
        self._top = None

    def is_empty(self):
        return self._top is None

    def top(self):
        if self.is_empty():
            raise StackUnderflow("in LStack.top()")
        return self._top.elem

    def push(self, elem):
        self._top = Node(elem, self._top)

    def pop(self):
        if self.is_empty():
            raise StackUnderflow("in LStack.pop()")
        result = self._top.elem
        self._top = self._top.next
        return result



if __name__=="__main__":
    st1 = SStack()
    st1.push(3)
    st1.push(5)
    while not st1.is_empty():
        print(st1.pop())

    print("============")
    st2 = LStack()
    st2.push(3)
    st2.push(5)
    while not st2.is_empty():
        print(st2.pop())