232. Implement Queue using Stacks | 用栈实现队列的功能

最新推荐文章于 2024-04-02 21:47:49 发布

原创最新推荐文章于 2024-04-02 21:47:49 发布 · 274 阅读

0 ·

CC 4.0 BY-SA版权

LeetCode 专栏收录该内容

57 篇文章

订阅专栏

本文介绍了一种利用两个栈来实现队列的方法。通过这种方式，可以有效地完成队列的基本操作，如push、pop、peek及判断队列是否为空等。文章提供了一个具体的Java实现示例。

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).

Subscribe to see which companies asked this question.

思路：用两个栈实现，一个用于输入stack1，一个用于输出stack2，在从stack1转移到stack2时，要注意，只有当stack2为空时才能转移，不然顺序会乱掉。

public class MyQueue {

		Stack<Integer> stack1;
		Stack<Integer> stack2;

		/** Initialize your data structure here. */
		public MyQueue() {
			stack1 = new Stack<>();
			stack2 = new Stack<>();
		}

		/** Push element x to the back of queue. */
		public void push(int x) {
			stack1.push(x);
		}

		/**
		 * Removes the element from in front of queue and returns that element.
		 */
		public int pop() {
			peek();

			return stack2.pop();
		}

		/** Get the front element. */
		public int peek() {
			if (stack2.isEmpty()) {
				while (!stack1.isEmpty()) {
					stack2.push(stack1.pop());
				}
			}
			return stack2.peek();
		}

		/** Returns whether the queue is empty. */
		public boolean empty() {
			return stack1.isEmpty() && stack2.isEmpty();
		}
	}
/**
 * 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();
 * boolean param_4 = obj.empty();
 */