120 lines
3.2 KiB
Java
120 lines
3.2 KiB
Java
/*
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* File: array_queue.java
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* Created Time: 2022-11-25
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* Author: Krahets (krahets@163.com)
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*/
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package chapter_stack_and_queue;
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import java.util.*;
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/* 基于环形数组实现的队列 */
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class ArrayQueue {
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int[] nums; // 用于存储队列元素的数组
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int size = 0; // 队列长度（即元素个数）
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int front = 0; // 头指针，指向队首
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int rear = 0; // 尾指针，指向队尾 + 1
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public ArrayQueue(int capacity) {
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// 初始化数组
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nums = new int[capacity];
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}
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/* 获取队列的容量 */
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public int capacity() {
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return nums.length;
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}
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/* 获取队列的长度 */
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public int size() {
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int capacity = capacity();
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// 由于将数组看作为环形，可能 rear < front ，因此需要取余数
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return (capacity + rear - front) % capacity;
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}
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/* 判断队列是否为空 */
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public boolean isEmpty() {
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return rear - front == 0;
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}
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/* 入队 */
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public void offer(int num) {
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if (size() == capacity()) {
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System.out.println("队列已满");
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return;
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}
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// 尾结点后添加 num
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nums[rear] = num;
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// 尾指针向后移动一位，越过尾部后返回到数组头部
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rear = (rear + 1) % capacity();
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}
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/* 出队 */
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public int poll() {
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// 删除头结点
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if (isEmpty())
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throw new EmptyStackException();
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int num = nums[front];
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// 队头指针向后移动，越过尾部后返回到数组头部
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front = (front + 1) % capacity();
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return num;
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}
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/* 访问队首元素 */
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public int peek() {
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// 删除头结点
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if (isEmpty())
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throw new EmptyStackException();
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return nums[front];
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}
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public int[] toArray() {
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int size = size();
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int capacity = capacity();
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// 仅转换有效长度范围内的列表元素
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int[] arr = new int[size];
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for (int i = 0, j = front; i < size; i++, j++) {
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arr[i] = nums[j % capacity];
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}
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return arr;
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}
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}
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public class array_queue {
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public static void main(String[] args) {
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/* 初始化队列 */
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int capacity = 10;
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ArrayQueue queue = new ArrayQueue(capacity);
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/* 元素入队 */
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queue.offer(1);
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queue.offer(3);
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queue.offer(2);
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queue.offer(5);
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queue.offer(4);
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System.out.println("队列 queue = " + Arrays.toString(queue.toArray()));
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/* 访问队首元素 */
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int peek = queue.peek();
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System.out.println("队首元素 peek = " + peek);
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/* 元素出队 */
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int poll = queue.poll();
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System.out.println("出队元素 poll = " + poll + "，出队后 queue = " + Arrays.toString(queue.toArray()));
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/* 获取队列的长度 */
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int size = queue.size();
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System.out.println("队列长度 size = " + size);
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/* 判断队列是否为空 */
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boolean isEmpty = queue.isEmpty();
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/* 测试环形数组 */
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for (int i = 0; i < 10; i++) {
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queue.offer(i);
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queue.poll();
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System.out.println("第 " + i + " 轮入队+出队后 queue = " + Arrays.toString(queue.toArray()));
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}
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}
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}
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