java代码如何实现队列的双端操作 java代码双端队列的基础实现技巧​

java.util.Deque

import java.util.ArrayDeque;
import java.util.Deque;

public class ArrayDequeExample {

    public static void main(String[] args) {
        Deque<String> deque = new ArrayDeque<>();

        // 从队头添加元素
        deque.addFirst("Element 1");
        deque.offerFirst("Element 0"); // offerFirst不会抛出异常，如果队列满了会返回false

        // 从队尾添加元素
        deque.addLast("Element 2");
        deque.offerLast("Element 3");

        System.out.println("Deque: " + deque); // 输出: Deque: [Element 0, Element 1, Element 2, Element 3]

        // 从队头移除元素
        String first = deque.removeFirst(); // 如果队列为空，会抛出NoSuchElementException
        String firstOrNull = deque.pollFirst(); // 如果队列为空，返回null

        // 从队尾移除元素
        String last = deque.removeLast(); // 如果队列为空，会抛出NoSuchElementException
        String lastOrNull = deque.pollLast(); // 如果队列为空，返回null

        System.out.println("Removed first: " + first); // 输出: Removed first: Element 0
        System.out.println("Removed last: " + last); // 输出: Removed last: Element 3
        System.out.println("Deque after removals: " + deque); // 输出: Deque after removals: [Element 1, Element 2]

        // 检查队列头部元素但不移除
        String peekFirst = deque.peekFirst();
        String getFirst = deque.getFirst();

        // 检查队列尾部元素但不移除
        String peekLast = deque.peekLast();
        String getLast = deque.getLast();

        System.out.println("Peek First: " + peekFirst); // 输出: Peek First: Element 1
        System.out.println("Peek Last: " + peekLast); // 输出: Peek Last: Element 2
    }
}

import java.util.Deque;
import java.util.LinkedList;

public class LinkedListDequeExample {

    public static void main(String[] args) {
        Deque<String> deque = new LinkedList<>();

        deque.addFirst("A");
        deque.addLast("B");
        deque.push("C"); // 等价于 addFirst
        deque.offer("D"); // 等价于 addLast

        System.out.println("Deque: " + deque); // 输出: Deque: [C, A, B, D]

        System.out.println("Removed first: " + deque.removeFirst()); // 输出: Removed first: C
        System.out.println("Removed last: " + deque.removeLast()); // 输出: Removed last: D
        System.out.println("Deque after removals: " + deque); // 输出: Deque after removals: [A, B]

        System.out.println("Peek first: " + deque.peekFirst()); // 输出: Peek first: A
        System.out.println("Peek last: " + deque.peekLast()); // 输出: Peek last: B

    }
}