【数据结构】队列

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前言

一、队列的介绍

队列是一种常见的数据结构，可以用来存储和管理一组元素。它有点像我们平时排队等待服务的场景，比如我们去超市买东西，我们会在收银台前排队，先来的人先服务，后来的人排在后面等待服务。
队列遵循这种先进先出（First-In-First-Out，FIFO）的原则。也就是说，先添加到队列中的元素，也会先被取出来。

二、队列的实现

总览
这里采用两个结构体的原因：由于设置头指针(head)和尾指针(tail)
，如果不再设置一个结构体来封装这两个指针，之后传参会很麻烦。

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Queue.h

#pragma once

#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<stdbool.h>

typedef int QDateType;

typedef struct QueueNode
{
	QDateType date;
	struct QueueNode* next;
}QN;

typedef struct Queue
{
	QN* head;
	QN* tail;
}Queue;

void QueueInit(Queue* ps);
void QueueDestroy(Queue* ps);
void QueuePush(Queue* ps, QDateType x);
void QueuePop(Queue* ps);
//返回头节点的数据
QDateType QueueFront(Queue* ps);
//返回尾节点的数据
QDateType QueueBack(Queue* ps);
int QueueSize(Queue* ps);
bool QueueEmpty(Queue* ps);
void QueuePrint(Queue* ps);

Queue.c

#define _CRT_SECURE_NO_WARNINGS 1
#include "Queue.h"

void QueueInit(Queue* ps)
{
	assert(ps);
	ps->head = NULL;
	ps->tail = NULL;
}

void QueueDestroy(Queue* ps)
{
	assert(ps);
	QN* cur = ps->head;
	while (cur != NULL)
	{
		Queue* next = cur->next;
		free(cur);
		cur = next;
	}
	ps->head = ps->tail = NULL;
}

void QueuePush(Queue* ps, QDateType x)
{
	assert(ps);
	QN* newnode = (QN*)malloc(sizeof(QN));
	assert(newnode);
	newnode->date = x;
	newnode->next = NULL;

	if (ps->head == NULL)
	{
		ps->head = ps->tail = newnode;
	}
	else
	{
		ps->tail->next = newnode;
		ps->tail = newnode;
	}
}

void QueuePop(Queue* ps)
{
	assert(ps);
	assert(!QueueEmpty(ps));//判断是否为空
	QN* next = ps->head->next;
	free(ps->head);
	ps->head = next;
	if (ps->head == NULL)
	{
		ps->tail = NULL;
	}
}

QDateType QueueFront(Queue* ps)
{
	assert(ps);
	assert(!QueueEmpty(ps));
	return ps->head->date;
}

QDateType QueueBack(Queue* ps)
{
	assert(ps);
	assert(!QueueEmpty(ps));
	return ps->tail->date;
}

int QueueSize(Queue* ps)
{
	assert(ps);
	int count = 0;
	QN* cur = ps->head;
	while (cur != NULL)
	{
		cur = cur->next;
		count++;
	}
	return count;
}

bool QueueEmpty(Queue* ps)
{
	assert(ps);
	return ps->head == NULL;
}

void QueuePrint(Queue* ps)
{
	assert(ps);
	QN* cur = ps->head;
	while (cur != NULL)
	{
		printf("%d ", cur->date);
		cur = cur->next;
	}
	if (ps->head != NULL)
	{
		printf("\n");
	}
	printf("队列大小为%d\n", QueueSize(ps));
}

Test.c

#define _CRT_SECURE_NO_WARNINGS 1
#include "Queue.h"

//队列 - 链表
//前出后进

void test()
{
	Queue s;
	QueueInit(&s);
	QueuePush(&s, 3);
	QueuePush(&s, 9);
	QueuePush(&s, 5);
	QueuePush(&s, 2);
	QueuePush(&s, 1);
	printf("队列头数据为%d\n", QueueFront(&s));
	printf("队列尾数据为%d\n", QueueBack(&s));
	
	//等价于QueuePrint(&s);
	while (!QueueEmpty(&s))
	{
		QDateType front = QueueFront(&s);
		printf("%d ", front);
		QueuePop(&s);
	}
	printf("\n");
	

	

	QueueDestroy(&s);
}
int main(void)
{
	test();
	return 0;
}