我对编码很陌生，我正试图在双链表上使用插入排序算法用C编写一个函数。该函数从旧列表中取出一个元素，并按字母顺序将其插入到新列表中。
当一个元素大于新/排序列表中的第一个元素时(即在字母表中更靠前(，我在循环函数时遇到了问题。现在，它只添加可以附加或前置的元素。为什么会这样？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);
}
以下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==
我认为你做了很多不必要的alloc/free。
从原始列表中删除项目时，不需要解除分配，只需调整head指针即可。
找到插入点后，可以将此节点直接插入到目标列表中。
这大大简化了代码。但是，您的基本列表基元不适合这种类型的从列表到列表的节点传输。
我已经编写了一些函数，这些函数可以直接用于将现有节点指针插入列表。
我还重构了排序函数以使用这些。
注意：因为您没有发布所有代码，所以我没有一个方便的方法来测试它。它会编译，但除此之外，没有任何保证。希望它能帮助你走得更远。
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;
}