232. Implement Queue using Stacks

最新推荐文章于 2023-10-09 00:28:50 发布

xdhc304

最新推荐文章于 2023-10-09 00:28:50 发布

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本文介绍了一种使用两个栈来实现队列数据结构的方法。通过巧妙地切换元素在两个栈之间的移动，可以实现队列的基本操作：push、pop、peek和empty。这种实现方式在某些场景下可以提供比传统队列更高效的操作。

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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.

Example:

MyQueue queue = new MyQueue();

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

class MyQueue {  
    
    Stack<Integer> s1 = new Stack<>();
    Stack<Integer> s2 = new Stack<>();
    /** Initialize your data structure here. */
    public MyQueue() {
    }
    
    /** Push element x to the back of queue. */
    public void push(int x) {
        while(!s2.empty()){
            s1.push(s2.pop());
        }
        s1.push(x);
    }
    
    /** Removes the element from in front of queue and returns that element. */
    public int pop() {
        while(!s1.empty()){
            s2.push(s1.pop());
        }
        return s2.pop();
    }
    
    /** Get the front element. */
    public int peek() {
        while(!s1.empty()){
            s2.push(s1.pop());
        }
        return s2.peek();
    }
    
    /** Returns whether the queue is empty. */
    public boolean empty() {
        return s2.empty() && s1.empty();
    }
}