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from __future__ import annotations

from typing import Generic, TypeVar

T = TypeVar("T")


class StackOverflowError(BaseException):
    pass


class StackUnderflowError(BaseException):
    pass


class Stack(Generic[T]):
    """A stack is an abstract data type that serves as a collection of
    elements with two principal operations: push() and pop(). push() adds an
    element to the top of the stack, and pop() removes an element from the top
    of a stack. The order in which elements come off of a stack are
    Last In, First Out (LIFO).
    https://en.wikipedia.org/wiki/Stack_(abstract_data_type)
    """

    def __init__(self, limit: int = 10):
        self.stack: list[T] = []
        self.limit = limit

    def __bool__(self) -> bool:
        return bool(self.stack)

    def __str__(self) -> str:
        return str(self.stack)

    def push(self, data: T) -> None:
        """
        Push an element to the top of the stack.

        >>> S = Stack(2) # stack size = 2
        >>> S.push(10)
        >>> S.push(20)
        >>> print(S)
        [10, 20]

        >>> S = Stack(1) # stack size = 1
        >>> S.push(10)
        >>> S.push(20)
        Traceback (most recent call last):
        ...
        data_structures.stacks.stack.StackOverflowError

        """
        if len(self.stack) >= self.limit:
            raise StackOverflowError
        self.stack.append(data)

    def pop(self) -> T:
        """
        Pop an element off of the top of the stack.

        >>> S = Stack()
        >>> S.push(-5)
        >>> S.push(10)
        >>> S.pop()
        10

        >>> Stack().pop()
        Traceback (most recent call last):
            ...
        data_structures.stacks.stack.StackUnderflowError
        """
        if not self.stack:
            raise StackUnderflowError
        return self.stack.pop()

    def peek(self) -> T:
        """
        Peek at the top-most element of the stack.

        >>> S = Stack()
        >>> S.push(-5)
        >>> S.push(10)
        >>> S.peek()
        10

        >>> Stack().peek()
        Traceback (most recent call last):
            ...
        data_structures.stacks.stack.StackUnderflowError
        """
        if not self.stack:
            raise StackUnderflowError
        return self.stack[-1]

    def is_empty(self) -> bool:
        """
        Check if a stack is empty.

        >>> S = Stack()
        >>> S.is_empty()
        True

        >>> S = Stack()
        >>> S.push(10)
        >>> S.is_empty()
        False
        """
        return not bool(self.stack)

    def is_full(self) -> bool:
        """
        >>> S = Stack()
        >>> S.is_full()
        False

        >>> S = Stack(1)
        >>> S.push(10)
        >>> S.is_full()
        True
        """
        return self.size() == self.limit

    def size(self) -> int:
        """
        Return the size of the stack.

        >>> S = Stack(3)
        >>> S.size()
        0

        >>> S = Stack(3)
        >>> S.push(10)
        >>> S.size()
        1

        >>> S = Stack(3)
        >>> S.push(10)
        >>> S.push(20)
        >>> S.size()
        2
        """
        return len(self.stack)

    def __contains__(self, item: T) -> bool:
        """
        Check if item is in stack

        >>> S = Stack(3)
        >>> S.push(10)
        >>> 10 in S
        True

        >>> S = Stack(3)
        >>> S.push(10)
        >>> 20 in S
        False
        """
        return item in self.stack


def test_stack() -> None:
    """
    >>> test_stack()
    """
    stack: Stack[int] = Stack(10)
    assert bool(stack) is False
    assert stack.is_empty() is True
    assert stack.is_full() is False
    assert str(stack) == "[]"

    try:
        _ = stack.pop()
        raise AssertionError  # This should not happen
    except StackUnderflowError:
        assert True  # This should happen

    try:
        _ = stack.peek()
        raise AssertionError  # This should not happen
    except StackUnderflowError:
        assert True  # This should happen

    for i in range(10):
        assert stack.size() == i
        stack.push(i)

    assert bool(stack)
    assert not stack.is_empty()
    assert stack.is_full()
    assert str(stack) == str(list(range(10)))
    assert stack.pop() == 9
    assert stack.peek() == 8

    stack.push(100)
    assert str(stack) == str([0, 1, 2, 3, 4, 5, 6, 7, 8, 100])

    try:
        stack.push(200)
        raise AssertionError  # This should not happen
    except StackOverflowError:
        assert True  # This should happen

    assert not stack.is_empty()
    assert stack.size() == 10

    assert 5 in stack
    assert 55 not in stack


if __name__ == "__main__":
    test_stack()

    import doctest

    doctest.testmod()
关于此算法

栈是一种基本线性数据结构,遵循访问对象的顺序。该顺序称为 LIFO(后进先出)或 FILO(先进后出)。栈的完美示例包括食堂的盘子、一堆书籍或一盒乐事薯片等。栈用于实现解析器和表达式求值以及回溯算法。基本操作是将元素压入栈和将元素弹出栈。我们可以使用链表或数组列表。栈只包含一个指针“顶部指针”,它指向栈的最顶层元素。插入和删除只发生在栈的一端。

标准栈操作

  1. push():将元素插入栈顶。
  2. pop():当我们删除栈顶元素时。
  3. isEmpty():它确定栈是否为空。
  4. isFull():确定栈是否已满。
  5. peek():获取栈顶元素的值,但不将其移除。

使用栈

一个名为 TOP 的指针用于跟踪栈中的顶部元素。在初始化栈时,我们将它的值设置为 -1,以便我们可以通过比较 TOP == -1 来检查栈是否为空。在压入元素时,我们增加 TOP 的值并将新元素放置在 TOP 指向的位置。在弹出元素时,我们返回 TOP 指向的元素并减少它的值。在压入之前,我们检查栈是否已满,在弹出之前,我们检查栈是否为空。

来源

  1. 栈数据结构 - GeeksForGeeks
  2. DS-栈 JavaPoint
  3. 栈数据结构

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