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