Implement Stack using Queues

最新推荐文章于 2021-02-28 14:00:39 发布

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最新推荐文章于 2021-02-28 14:00:39 发布

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本文介绍了一种使用两个队列来模拟栈数据结构的方法。通过将元素压入其中一个队列并随后将其转移至另一个队列的方式，实现了栈的基本操作：push、pop、top以及判断是否为空。这种方式确保了所有操作的有效性，并且可以方便地应用于不直接支持栈的数据环境中。

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Implement the following operations of a stack using queues.

push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
empty() -- Return whether the stack is empty.

Notes:

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

class Stack {
public:
    queue<int> queue1;
    queue<int> queue2;
    // Push element x onto stack.
    void push(int x) {
        if(queue1.empty()){
            queue1.push(x);
            while(!queue2.empty()){
                queue1.push(queue2.front());
                queue2.pop();
            }
        }else{
            queue2.push(x);
            while(!queue1.empty()){
                queue2.push(queue1.front());
                queue1.pop();
            }
        }
    }

    // Removes the element on top of the stack.
    void pop() {
        if(!queue1.empty()){
            queue1.pop();
        }else{
            queue2.pop();
        }
    }

    // Get the top element.
    int top() {
        if(!queue1.empty()){
            return queue1.front();
        }else{
            return queue2.front();
        }
    }

    // Return whether the stack is empty.
    bool empty() {
        if(queue1.empty() && queue2.empty()){
            return true;
        }else{
            return false;
        }
    }
};