队列的实现和实际运用

2023-11-20 23:10:05

队列可以以不同的方式来实现。最常见的实现是使用数组或链表。

使用数组实现队列

使用数组实现队列的优点是简单易懂。队列的元素存储在一个连续的内存空间中，因此可以很容易地通过索引来访问元素。

public class ArrayQueue {

    private int[] items;
    private int head;
    private int tail;
    private int size;

    public ArrayQueue(int capacity) {
        items = new int[capacity];
        head = 0;
        tail = -1;
        size = 0;
    }

    public void enqueue(int item) {
        if (isFull()) {
            throw new IllegalStateException();
        }
        tail = (tail + 1) % items.length;
        items[tail] = item;
        size++;
    }

    public int dequeue() {
        if (isEmpty()) {
            throw new IllegalStateException();
        }
        int item = items[head];
        head = (head + 1) % items.length;
        size--;
        return item;
    }

    public int peek() {
        if (isEmpty()) {
            throw new IllegalStateException();
        }
        return items[head];
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public boolean isFull() {
        return size == items.length;
    }

    public int size() {
        return size;
    }
}

使用链表实现队列

使用链表实现队列的优点是空间效率更高。队列的元素存储在不同的内存空间中，因此不需要连续的内存空间。

public class LinkedQueue {

    private Node head;
    private Node tail;
    private int size;

    public LinkedQueue() {
        head = null;
        tail = null;
        size = 0;
    }

    public void enqueue(int item) {
        Node newNode = new Node(item);
        if (isEmpty()) {
            head = newNode;
            tail = newNode;
        } else {
            tail.next = newNode;
            tail = newNode;
        }
        size++;
    }

    public int dequeue() {
        if (isEmpty()) {
            throw new IllegalStateException();
        }
        int item = head.data;
        head = head.next;
        if (head == null) {
            tail = null;
        }
        size--;
        return item;
    }

    public int peek() {
        if (isEmpty()) {
            throw new IllegalStateException();
        }
        return head.data;
    }

    public boolean isEmpty() {
        return size == 0;
    }

    public int size() {
        return size;
    }

    private class Node {

        private int data;
        private Node next;

        public Node(int data) {
            this.data = data;
            this.next = null;
        }
    }
}