Python堆栈重叠元素累加

Question

我想在Python中的Arraystack上累积添加元素

class StockManager:

    __PROFIT = 0

    def __init__(self, o_name, o_surname):
        self.box = ArrayStack()
        self._name = o_name
        self._surname = o_surname

    def buy_shares(self, company, number, buy_price):
        StockManager.__PROFIT -= buy_price * number
        n = 0

        if len(self.box) < 2:
            """there is no overlapped elements when box has no element"""
            self.box.push(company) 
            self.box.push(number)
        else:
            while n < len(self.box):
               if self.box._data[n] == company:
               """every even index(n = 0, 2, 4, ...) refers to company name"""
               """every odd index(n = 1, 3, 5, ...), which is next to even index refers to number of buying"""
                    self.box._data[n + 1] += number
                    n += 2

               elif self.box._data[n] != company:
                    """ if there's no overlapping, then just put the elements """
                    self.box.push(company)
                    self.box.push(number)
                    n += 2
        return print(self.box._data)

Arraystack 类是这样的:

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

    def __init__(self):
        """Create an empty stack."""
        self._data = []                       # nonpublic list instance

    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 push(self, e):
        """Add element e to the top of the stack."""
        self._data.append(e)                  # new item stored at end of list

    def top(self):
        """Return (but do not remove) the element at the top of the stack.

        Raise Empty exception if the stack is empty.
        """
        if self.is_empty():
            raise AssertionError('Stack is empty')
        return self._data[-1]                 # the last item in the list

    def pop(self):
        """Remove and return the element from the top of the stack (i.e., LIFO).

        Raise Empty exception if the stack is empty.
        """
        if self.is_empty():
            raise AssertionError('Stack is empty')
        return self._data.pop()               # remove last item from list

    def print_contents(self):
        print("Stack content: {0}".format(self._data))

当我运行stockmanager时

if __name__ == '__main__':
    P = StockManager("A","B")
    P.buy_shares("hyundai", 20, 100)
    P.buy_shares("hyundai", 20, 100)
    P.buy_shares("hyundai", 20, 100)
    P.buy_shares("lg", 20, 100)

结果是

['hyundai', 20]  => O.K
['hyundai', 40]  => O.K
['hyundai', 60]  => O.K
['hyundai', 60, 'lg', 40] => It should be ['hyundai', 60, 'lg', 20]
['hyundai', 60, 'lg', 60, 'lg', 40] => don't know why this result comes...

我该如何解决这个问题？

Answer 1

所以，问题出在你的while上循环:

           while n < len(self.box):
           if self.box._data[n] == company:
               """every even index(n = 0, 2, 4, ...) refers to company name"""
               """every odd index(n = 1, 3, 5, ...), which is next to even index refers to number of buying"""
               self.box._data[n + 1] += number
               n += 2

           elif self.box._data[n] != company:
               """ if there's no overlapping, then just put the elements """
               self.box.push(company)
               self.box.push(number)
               n += 2

想象一下我们已经跑了:

P = StockManager("A","B")
P.buy_shares("hyundai", 20, 100)
P.buy_shares("hyundai", 20, 100)
P.buy_shares("hyundai", 20, 100)

到目前为止，一切都按计划进行。现在，您尝试:

P.buy_shares("lg", 20, 100)

所以:n == 0和len(self.box) == 2 ，所以我们进入循环。

if条件失败，self.box._data[n] != 'lg' ，所以我们转到 elif block :

           self.box.push(company)
           self.box.push(number)
           n += 2

现在，box == ['hyundai', 60, 'lg', 20]和n == 2 。可是等等!循环条件为n < len(box) ，但是len(box) == 4 ，所以我们再次进入while循环!这次，if条件自 self.box._data[2] == 'lg' 起经过此时间.

因此，您执行 if block 的主体:

           self.box._data[n + 1] += number
           n += 2

现在，n == 4和box == ['hyundai', 60, 'lg', 40] 。这次，4 < len(box)失败，我们退出循环，您的函数也结束。

现在，堆栈对我来说似乎是错误的数据结构。必须将尺寸增加两倍，这很笨重。如果您真的想这样做，我建议采用类似的方法

offset = 0
i = -2
for i in range(0, len(self.box), 2):
    if self.box._data[n] == company:
        break
else:
    offset = 2
    self.box.push(company)
    self.box.push(0)
self.box._data[i + offset + 1] += number

但是，这又很笨拙。您最好使用 dict对于盒子，那么逻辑可以简单地实现为:

self.box[company] = self.box.get(company, 0) + 1

或者更好的是，使用 defaultdict

>>> from collections import defaultdict
>>> box = defaultdict(int)
>>> box
defaultdict(<class 'int'>, {})
>>> box['lg'] += 20
>>> box
defaultdict(<class 'int'>, {'lg': 20})
>>> box['lg'] += 20
>>> box
defaultdict(<class 'int'>, {'lg': 40})
>>> box['lg']
40