Implement Queue using Stacks

最新推荐文章于 2023-10-09 00:28:50 发布

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最新推荐文章于 2023-10-09 00:28:50 发布

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本文链接：https://blog.youkuaiyun.com/wangbao2111/article/details/50266319

本文介绍了一种使用两个栈来实现队列的方法。通过将入队操作映射为栈的压入操作，出队操作映射为从另一个栈中弹出元素的操作，实现了队列的基本功能：push、pop、peek及empty。此方法充分利用了栈的特点，避免了直接使用队列可能带来的额外开销。

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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.

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).

class Queue {
public:
    stack<int> stack1;
    stack<int> stack2;
    // Push element x to the back of queue.
    void push(int x) {
        stack1.push(x);
        
    }

    // Removes the element from in front of queue.
    void pop(void) {
        if(stack2.empty()){
            while(!stack1.empty()){
                stack2.push(stack1.top());
                stack1.pop();
            }
        }
        stack2.pop();
    }

    // Get the front element.
    int peek(void) {
        if(stack2.empty()){
            while(!stack1.empty()){
                stack2.push(stack1.top());
                stack1.pop();
            }
        }
        return stack2.top();
    }

    // Return whether the queue is empty.
    bool empty(void) {
        if(stack1.empty() && stack2.empty()){
            return true;
        }else{
            return false;
        }
    }
};