102 lines
3.3 KiB
Java
102 lines
3.3 KiB
Java
/*
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* The MIT License (MIT)
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*
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* Copyright © 2020 xrv <xrv@live.com>
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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package io.github.ehlxr.datastructure.queue;
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/**
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* 数组实现循环队列
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* <p>
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* 一般情况下只需要 tail + 1 == head 即可判定队列已满，结合特殊情况（head == 0，tail == n - 1）
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* 可使用公式 (tail + 1) % size == head 判定队列已满，head == tail 判断队列为空，
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* 但这种公式判断循环队列会浪费一个数组的存储空间。
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* <p>
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* 另也可使用一个变量 n 记录当前队列中的数量（入队 +1，出队 -1），当 head == tail 时，
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* 如果 n == size，则队列已满，如果 n == 0 则队列为空。
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*
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* @author ehlxr
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* @since 2021-12-25 21:01.
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*/
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public class CircularQueue {
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private final Integer[] data;
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private int head = 0;
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private int tail = 0;
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private final int size;
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public CircularQueue(int size) {
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data = new Integer[size];
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this.size = size;
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}
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public static void main(String[] args) {
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CircularQueue queue = new CircularQueue(5);
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// 循环队列会浪费一个数组的存储空间。队列容量为 5，入队 5 个最后一个失败
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for (int i = 0; i < 5; i++) {
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System.out.println(queue.enqueue(i));
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}
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// 出队 2 个，然后还可以入队 2 个
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for (int i = 0; i < 2; i++) {
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System.out.println(queue.dequeue());
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}
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System.out.println(queue.enqueue(7));
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System.out.println(queue.enqueue(8));
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System.out.println(queue.enqueue(9));
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// 出队 6 个，最后一个失败
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for (int i = 0; i < 6; i++) {
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System.out.println(queue.dequeue());
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}
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}
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/**
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* 入队（从队尾添加元素）
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*/
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public boolean enqueue(Integer item) {
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// 判断队列是否已满
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if ((tail + 1) % size == head) {
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return false;
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}
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data[tail] = item;
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tail = (tail + 1) % size;
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return true;
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}
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/**
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* 出队（从队首取出元素）
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*/
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public Integer dequeue() {
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// 判断队列是否为空
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if (head == tail) {
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return null;
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}
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Integer no = data[head];
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head = (head + 1) % size;
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return no;
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}
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}
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