232. Implement Queue using Stacks

最新推荐文章于 2024-06-30 02:03:55 发布

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最新推荐文章于 2024-06-30 02:03:55 发布

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本文介绍了一种使用栈来实现队列的方法。通过两个栈分别用于元素的输入和输出，实现了队列的基本操作：push、pop、peek以及判断队列是否为空。此方法巧妙地利用了栈的特点，有效地完成了队列的功能。

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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 MyQueue {
public:
    /** Initialize your data structure here. */
    stack<int> input,output;
    MyQueue() {
        
    }
    
    /** Push element x to the back of queue. */
    void push(int x) {
        input.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    int pop() {
        int value = peek();
        output.pop();
        return value;
    }
    
    /** Get the front element. */
    int peek() {
        if(output.empty())
            while(input.size())
            {
                output.push(input.top());
                input.pop();
            }
        return output.top();
        
    }
    
    /** Returns whether the queue is empty. */
    bool empty() {
        return input.empty() && output.empty();
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue obj = new MyQueue();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.peek();
 * bool param_4 = obj.empty();
 */