算法精解（C语言描述） 第5章 读书笔记

第5章

5.1 单链表

/*  -------------------------------- list.h --------------------------------  */
#ifndef LIST_H
#define LIST_H

#include <stdlib.h>

/*  Define a structure for linked list elements.*/
typedef struct ListElmt_ 
{
    void *data;
    struct ListElmt_ *next;
} ListElmt;

/*  Define a structure for linked lists.*/
typedef struct List_
{
    int size;
    int (*match)(const void *key1, const void *key2);
    void (*destroy)(void *data);
    ListElmt *head;
    ListElmt *tail;
} List;

/*  --------------------------- Public Interface ---------------------------  */
void list_init(List *list, void (*destroy)(void *data));//whl-?其destroy参数的用法？
void list_destroy(List *list);
int list_ins_next(List *list, ListElmt *element, const void *data);
int list_rem_next(List *list, ListElmt *element, void **data);

#define list_size(list) ((list)->size)
#define list_head(list) ((list)->head)
#define list_tail(list) ((list)->tail)
#define list_is_head(list, element) ((element) == (list)->head ? 1 : 0)
#define list_is_tail(element) ((element)->next == NULL ? 1 : 0)
#define list_data(element) ((element)->data)
#define list_next(element) ((element)->next)

#endif

/*  -------------------------------- list.c --------------------------------  */
#include <stdlib.h>
#include <string.h>
#include "list.h"
/*  ------------------------------- list_init ------------------------------  */
void list_init(List *list, void (*destroy)(void *data))//若链表包含不该释放的数据，则destroy应设置为NULL
{
    /*  Initialize the list. */
    list->size = 0;
    list->destroy = destroy;//把函数指针成员destroy设置为定义的析构函数
    list->head = NULL;
    list->tail = NULL;
    return;
}
/*  ----------------------------- list_destroy -----------------------------  */
void list_destroy(List *list)//若传给list_init的参数destroy不为NULL，则移除链表中每个元素时都调用该函数一次
{
    void *data;
    /*  Remove each element. */
    while (list_size(list) > 0)
    {
        if (list_rem_next(list, NULL, (void **)&data) == 0 && list->destroy != NULL)
        {
            /*  Call a user-defined function to free dynamically allocated data.    */
            list->destroy(data);
        }
    }
    /*  No operations are allowed now, but clear the structure as a precaution.   */
    memset(list, 0, sizeof(List));
    return;
}
/*  ----------------------------- list_ins_next ----------------------------  */
int list_ins_next(List *list, ListElmt *element, const void *data) //在list指定的链表中element后面插入一个新元素
{
    ListElmt *new_element;
    /*  Allocate storage for the element. */
    if ((new_element = (ListElmt *)malloc(sizeof(ListElmt))) == NULL)
    {
        return -1;
    }
    /*  Insert the element into the list. */
    //new_element->data = (void *)data;
    new_element->data = (void *)data;
    if (element == NULL) //若element设置为NULL，则新元素插入链表头部
    {
        /*  Handle insertion at the head of the list. */
        if (list_size(list) == 0)
            list->tail = new_element;
        new_element->next = list->head;
        list->head = new_element;
    }
    else 
    {
        /*  Handle insertion somewhere other than at the head. */
        if (element->next == NULL)
            list->tail = new_element;
        new_element->next = element->next;
        element->next = new_element;
    }
    /*  Adjust the size of the list to account for the inserted element. */
    list->size++;
    return 0;
}
/*  ----------------------------- list_rem_next ----------------------------  */
int list_rem_next(List *list, ListElmt *element, void **data)//移除由list指定的链表中element后的那个元素
{
    ListElmt *old_element;

    /*  Do not allow removal from an empty list. */
    if (list_size(list) == 0)
        return -1;

    /*  Remove the element from the list. */
    if (element == NULL)//若element设置为NULL，则移除链表头部元素
    {
        /*  Handle removal from the head of the list. */
        *data = list->head->data;
        old_element = list->head;
        list->head = list->head->next;
        if (list_size(list) == 1)
            list->tail = NULL;
    }
    else {
        /*  Handle removal from somewhere other than the head. */
        if (element->next == NULL)
            return -1;
        *data = element->next->data;
        old_element = element->next;
        element->next = element->next->next;
        if (element->next == NULL)
            list->tail = element;
    }
    /*  Free the storage allocated by the abstract data type. */
    free(old_element);
    /*  Adjust the size of the list to account for the removed element. */
    list->size--;
    return 0;
}