ARTS #62 | 不要只顾低头赶路

Algorithm

规则如下：

Implement the following operations of a queue using stacks.

push(x) – Push element x to the back of queue.
pop() – Removes the element from in front of queue.
peek() – Get the front element.
empty() – Return whether the queue is empty.

Example:

MyQueue queue = new MyQueue();

queue.push(1);
queue.push(2);  
queue.peek();  // returns 1
queue.pop();   // returns 1
queue.empty(); // returns false

Notes:

You must use only standard operations of a stack – which means only push to top, peek/pop from top, size, and is empty operations are valid.
Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

Solution

class MyQueue:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.stack = []
        self.reverse_stack = []

    def push(self, x: int) -> None:
        """
        Push element x to the back of queue.
        """
        self.stack.append(x)

    def pop(self) -> int:
        """
        Removes the element from in front of queue and returns that element.
        """
        self.peek()
        return self.reverse_stack.pop()

    def peek(self) -> int:
        """
        Get the front element.
        """
        if not self.reverse_stack:
            while self.stack:
                self.reverse_stack.append(self.stack.pop())
        
        return self.reverse_stack[-1]

    def empty(self) -> bool:
        """
        Returns whether the queue is empty.
        """
        return not (self.stack or self.reverse_stack)

很简单的题目。

Review

Static Dispatch Over Dynamic Dispatch

喜欢这类文章：有观点有验证。

其中观点有：

final - 从不被动态派发
private - 编译将对标记为该关键字的所有变量和方法执行搜索，如果找到 override 的地方将生成编译错误；如果找不到任何 override 行为，则隐式将其标记为 final
Whole-Module - 有之前的 ARTS 作业中有一篇关于它的说明：传送门

Tip

简单两步为自己的网站添加 fancybox 大图预览效果:

添加 jQuery 和 fancybox 文件

为所有 img 元素添加父元素

$("img").each(function () {
    var element = document.createElement("a");
    $(element).attr("data-fancybox", "gallery");
    $(element).attr("href", $(this).attr("src"));
    $(this).wrap(element);
});

无论如何，请不要只知道低头赶路，沦为一个终生的做题家。

Algorithm

Solution

Review

Tip

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