c - c中使用双向链表的插入排序算法——插入节点

Question

我是编码的新手，我正在尝试使用双向链表上的插入排序算法在 C 中编写一个函数。该函数从旧列表中取出一个元素并将其按字母顺序插入到新列表中。

当元素大于(即在字母表中更远)新/排序列表中的第一个元素时，我在循环函数时遇到问题。现在它只添加可以附加或前置的元素。为什么是这样？这是我的功能:

    #include "sort.h"
    #include <stdio.h>
    #include <stdlib.h>
    #include "linked_list.h"

/* sort linked list *list using merge insertion sort. */
/* upon success, the elements in *list will be sorted. */
/* return silently if *list is uninitialised or empty. */
/* the compare argument is a pointer to a function which returns */
/* less than 0, 0, or greater than 0 if first argument is */
/* less than, equal to, or greater than second argument respectively. */
void insertion_sort(LinkedList *list, int (*compare)(void *, void *))
{
    void *d, *B_node_data;
    LinkedList *B;
    Node *B_node, *new_node;

    if(!list)
        return;

    if(!list->head)
        return;

    B = initialise_linked_list();
    d = list->head->data;
    remove_head_linked_list(list);
    prepend_linked_list(B, d);


    while(list->head)
    {
        d = list->head->data;
        B_node = B->head;
        remove_head_linked_list(list);

        while(B_node)
        {
        B_node_data = B_node->data;
            if((*compare)(d, B_node_data) <= 0)
            {
                if(B_node->prev)
                {
                    new_node = initialise_node();
                    new_node->next = B_node;
                    new_node->prev = B_node->prev;
                    new_node->data = d;
                    break;
                }
                if(B->head->data == B_node_data)
                {
                    prepend_linked_list(B, d);
                    break;
                }
            }                    
            if(!B_node->next)
                append_linked_list(B, d);
        else{
                B_node = B_node->next;
            }
        }
    } 
list->head = B->head; 
list->tail = B->tail;

B->head = NULL;
B->tail = NULL;
free_linked_list(B);


}

这里是我从另一个文件调用的函数的定义:

    #include "linked_list.h"

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

Node *initialise_node(void)
{
    Node *node;

    if(!(node = (Node *) malloc(sizeof(Node)))) {
        fprintf(stderr, "error: unable to initialise node.\n");
        exit(EXIT_FAILURE);
    }
    node->next = node->prev = node->data = NULL;

    return node;
}

void free_node(Node *node)
{
    if(!node)
        return;
    free(node);
}

LinkedList *initialise_linked_list(void)
{
    LinkedList *list;

    if(!(list = (LinkedList *) malloc(sizeof(LinkedList)))) {
        fprintf(stderr, "error: unable to initialise linked list.\n");
        exit(EXIT_FAILURE);
    }
    list->head = list->tail = NULL;

    return list;
}

void free_linked_list(LinkedList *list)
{
    Node *next;

    while(list->head) {
        next = list->head->next;
        free_node(list->head);
        list->head = next;
    }
    free(list);
}

void append_linked_list(LinkedList *list, void *data)
{
    Node *node;

    node = initialise_node();

    node->data = data;
    node->prev = list->tail;
    if(list->tail) {
        list->tail->next = node;
    }
    list->tail = node;
    if(!list->head)
        list->head = node;
}

void prepend_linked_list(LinkedList *list, void *data)
{
    Node *node;

    node = initialise_node();

    node->data = data;
    node->next = list->head;
    if(list->head) {
        list->head->prev = node;
    }
    list->head = node;
    if(!list->tail)
        list->tail = node;
}

void remove_head_linked_list(LinkedList *list)
{
    Node *head;

    if(!list->head)
        return;
    head = list->head->next;
    free(list->head);
    list->head = head;
    if(list->head)
        list->head->prev = NULL;
    else
        list->tail = NULL;

}

void remove_tail_linked_list(LinkedList *list)
{
    Node *tail;

    if(!list->tail)
        return;
    tail = list->tail->prev;
    free_node(list->tail);
    list->tail = tail;
    if(list->tail)
        list->tail->next = NULL;
    else
        list->head = NULL;
}

这是我的输出

==942== Command: ./task1_test harmonious pencil push naive jittery 
greedy billowy practise lock star appear record precede pen lace
==942== 
appear
billowy
greedy
harmonious
pencil
push
star
==942== 
==942== HEAP SUMMARY:
==942==     in use at exit: 264 bytes in 11 blocks
==942==   total heap usage: 35 allocs, 24 frees, 824 bytes allocated
==942== 
==942== 264 bytes in 11 blocks are definitely lost in loss record 1 of 1
==942==    at 0x4C29C23: malloc (vg_replace_malloc.c:299)
==942==    by 0x40084E: initialise_node (linked_list.c:11)
==942==    by 0x400CF1: insertion_sort (sort.c:43)
==942==    by 0x400815: main (task1_test.c:33)
==942== 
==942== LEAK SUMMARY:
==942==    definitely lost: 264 bytes in 11 blocks
==942==    indirectly lost: 0 bytes in 0 blocks
==942==      possibly lost: 0 bytes in 0 blocks
==942==    still reachable: 0 bytes in 0 blocks
==942==         suppressed: 0 bytes in 0 blocks
==942== 

Answer 1

我认为您正在做很多不必要的分配/释放。

当从原始列表中取出一个项目时，不需要释放它，只需调整head指针即可。

当找到插入点后，可以直接将该节点插入到目标列表中。

这大大简化了代码。但是，您的基本列表基元不适合这种从列表到列表的节点传输。

我编写了一些函数，可以直接将现有节点指针插入到列表中。

我还重构了排序函数以使用它们。

注意:因为您没有发布所有 代码，所以我没有方便的方法来测试它。它会编译，但除此之外，没有任何保证。希望它能帮助您走得更远。

void
insert_list_tail(LinkedList *list,Node *new)
{
    Node *prev;

    prev = list->tail;

    if (prev != NULL)
        prev->next = new;

    new->next = NULL;
    new->prev = prev;

    list->tail = new;

    if (list->head == prev)
        list->head = new;
}

void
insert_list_head(LinkedList *list,Node *new)
{
    Node *next;

    next = list->head;

    if (next != NULL)
        next->prev = new;

    new->prev = NULL;
    new->next = next;

    list->head = new;

    if (list->tail == next)
        list->tail = new;
}

void
insert_list_before(LinkedList *list,Node *cur,Node *new)
{
    Node *next;
    Node *prev;

    do {
        // we got to the end of the list without an insert before point, so
        // append to tail of list
        if (cur == NULL) {
            insert_list_tail(list,new);
            break;
        }

        // we do insert after [internally here] so get the previous node
        cur = cur->prev;

        // with no previous node insert at head of list
        if (cur == NULL) {
            insert_list_head(list,new);
            break;
        }

        prev = cur->prev;
        next = cur->next;

        if (prev != NULL)
            prev->next = new;
        else
            list->head = new;

        if (next != NULL)
            next->prev = new;
        else
            list->tail = new;

        new->prev = prev;
        new->next = next;
    } while (0);
}

void
insertion_sort(LinkedList *slist, int (*compare)(void *,void *))
{
    LinkedList list;
    LinkedList *dlist = &list;
    Node *src;
    Node *dst;

    if (slist == NULL)
        return;

    if (slist->head == NULL)
        return;

    dlist->head = NULL;
    dlist->tail = NULL;

    // grab first source node and insert it at destination list head
    src = slist->head;
    slist->head = src->next;
    insert_list_head(dlist,src);

    while (1) {
        src = slist->head;
        if (src == NULL)
            break;

        slist->head = src->next;

        // find node to do an insertion before (i.e. find the first destination
        // node that is higher than the source node)
        for (dst = dlist->head;  dst != NULL;  dst = dst->next) {
            if (compare(dst->data,src->data) > 0)
                break;
        }

        insert_list_before(dlist,dst,src);
    }

    slist->head = dlist->head;
    slist->tail = dlist->tail;
}