数据结构(8) - 链式队列

链式队列，使用链表实现的队列存储结构，链式队列的实现思想同顺序队列类似，只需创建两个指针（命名为 top 和 rear）分别指向链表中队列的队头元素和队尾元素。

linked-queue.c

/**
 * C data structure linked queue example.
 * 
 * License - MIT.
*/

#include "linked-queue.h"


/**
 * linkqueue_isempty - Determine if the queue is empty.
*/
bool linkqueue_isempty(LPQUEUECURSOR lpcursor)
{
    return (lpcursor->front == lpcursor->rear);
}


/**
 * linkqueue_put - Put data to queue.
*/
int linkqueue_put(LPQUEUECURSOR lpcursor, int data)
{
    LPLINKQUEUE node = NULL;

    node = (LPLINKQUEUE) malloc(sizeof(LINKQUEUE));

    if (NULL == node) {
        printf("Error in queue put.\n");
        return -1;
    }

    /* Put data to queue. */
    node->data              = data;
    node->next              = lpcursor->rear->next;
    lpcursor->rear->next    = node;
    lpcursor->rear          = lpcursor->rear->next;

    return 0;
}


/**
 * linkqueue_get - Get data from queue.
*/
int linkqueue_get(LPQUEUECURSOR lpcursor, int *data)
{
    LPLINKQUEUE tmp;

    /* Determine if queue is empty. */
    if (linkqueue_isempty(lpcursor))
        return -1;

    /* Get data from queue. */
    tmp             = lpcursor->front;
    lpcursor->front = lpcursor->front->next;
    *data           = lpcursor->front->data;

    free(tmp);

    return 0;
}


/**
 * linkqueue_init - Initialize linked queue.
*/
int linkqueue_init(LPQUEUECURSOR *lpcursor)
{
    /* Allocate cursor memory space. */
    *lpcursor = (LPQUEUECURSOR) malloc(sizeof(QUEUECURSOR));

    if (NULL == *lpcursor) {
        printf("Error in queue init.\n");
        return -1;
    }

    /* Allocate head node memory space. */
    (*lpcursor)->front = (LPLINKQUEUE) malloc(sizeof(LINKQUEUE));

    if (NULL == (*lpcursor)->front) {
        printf("Error in queue init.\n");
        return -1;
    }

    (*lpcursor)->front->next    = NULL;
    (*lpcursor)->rear           = (*lpcursor)->front;

    return 0;
}


/**
 * linkqueue_clear - Clear linked queue.
*/
int linkqueue_clear(LPQUEUECURSOR lpcursor)
{
    int tmp = -1;

    while (!linkqueue_isempty(lpcursor))
    {
        linkqueue_get(lpcursor, &tmp);
    }

    free(lpcursor);
    lpcursor = NULL;

    return 0;
}

linked-queue.h

/**
 * C data structure linked queue example.
 * 
 * License - MIT.
*/

#ifndef __LINKED_QUEUE_H__
#define __LINKED_QUEUE_H__


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


typedef struct _LINKQUEUE {
    int data;
    struct _LINKQUEUE *next;
} LINKQUEUE, *LPLINKQUEUE;

typedef struct _QUEUECURSOR {
    LPLINKQUEUE front, rear;
} QUEUECURSOR, *LPQUEUECURSOR;


bool linkqueue_isempty (LPQUEUECURSOR lpcursor);
int linkqueue_put      (LPQUEUECURSOR lpcursor, int data);
int linkqueue_get      (LPQUEUECURSOR lpcursor, int *data);
int linkqueue_init     (LPQUEUECURSOR *lpcursor);
int linkqueue_clear    (LPQUEUECURSOR lpcursor);


#endif /* __LINKED_QUEUE_H__ */

mian.c

/**
 * C data structure linked queue example.
 * 
 * License - MIT.
*/

#include <stdio.h>

#include "linked-queue.h"


/**
 * queue_test - Test linked queue example.
*/
int queue_test(LPQUEUECURSOR lpcursor, int buf[], int len)
{
    int i = 0;
    int data = 0;

    printf("Put data: ");

    for (i = 0; i < len; i++) {
        linkqueue_put(lpcursor, buf[i]);
        printf("%d ", buf[i]);
    }

    printf("\nGet data: ");

    for (i = 0; i < len; i++) {
        linkqueue_get(lpcursor, &data);
        printf("%d ", data);
    }

    printf("\n");

    return 0;
}


/**
 * Main function.
*/
int main(void)
{
    int buf[5] = {1, 2, 3, 4, 5};
    LPQUEUECURSOR lpcursor = NULL;

    linkqueue_init(&lpcursor);

    queue_test(lpcursor, buf, 5);

    linkqueue_clear(lpcursor);

    return 0;
}

Makefile

# Makefile
CC = gcc
CFLAGS = -Wall -g -O0

SRC = main.c linked-queue.c

OBJ = linkqueue-test

$(OBJ) : $(SRC)
    $(CC) $(CFLAGS) -o $@ $^

clean:
    $(RM) $(OBJ) *.o *.*.sw?

 

详细代码请参考Github: [Link] [https://github.com/Phoebus-Ma/C-Helper/tree/main/Class-1/Queue.C].