LeetCode 225. Implement Stack using Queues

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本文介绍了一种使用队列来实现栈数据结构的方法。通过特殊的元素插入操作保证了栈顶元素始终位于队列的前端，从而实现了标准的栈操作：push、pop、top和empty。该方法仅使用队列的基本操作，适用于需要栈但只提供队列API的情况。

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mplement 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 onlypush to back, peek/pop from front, size, andis 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> myQueue;
void push(int x) {
    int n = myQueue.size();

    myQueue.push(x);
    for(int i = 0; i < n; i ++) {
        int tmp = myQueue.front();
        myQueue.pop();
        myQueue.push(tmp);
    }
}

// Removes the element on top of the stack.
void pop() {
    myQueue.pop();
}

// Get the top element.
int top() {
    return myQueue.front();
}

// Return whether the stack is empty.
bool empty() {
    return myQueue.empty();
}
};