[英]I am trying to reverse a linked list using recursion in C, I have some doubts on my recursive function
下面是程序
#include <stdio.h>
#include <stdlib.h>
struct node
{
int data;
struct node *next;
};
struct node *head;
struct node* reverse_ll(struct node* hnode)
{
if(hnode == 0)
{
return 0;
}
if(hnode->next == 0)
{
head=hnode;
return hnode;
}
struct node* ptr=reverse_ll(hnode->next);
ptr->next=hnode;
hnode->next=0;
//return hnode;
}
void display()
{
struct node *ptr;
ptr=head;
if(ptr==0)
{
printf("empty");
}
else
{
while(ptr!=0)
{
printf("%d->",ptr->data);
ptr=ptr->next;
}
printf("null");
}
}
int main()
{
struct node* h;
lastinsert(1);
lastinsert(2);
lastinsert(3);
lastinsert(4);
lastinsert(5);
display();
h=reverse_ll(head);
display();
return 0;
}
在 function reverse_ll() 中,即使我評論“返回 hnode”,我也得到了正確的 output 當我評論“返回 hnode”時,ptr 如何從哪里接收它的地址?
output:1->2->3->4->5->空 5->4->3->2->1->空
reverse_ll()
在遞歸情況下必須返回一個struct node *
:
#include <stdio.h>
#include <stdlib.h>
struct node {
int data;
struct node *next;
};
struct node *head;
void lastinsert(int data) {
struct node **c = &head;
for(; *c; c = &(*c)->next);
*c = malloc(sizeof(*head));
if (!(*c)) {
printf("malloc failed\n");
return;
}
(*c)->data = data;
(*c)->next = NULL;
}
struct node *reverse_ll(struct node* hnode) {
if(!hnode)
return NULL;
if(!hnode->next) {
head = hnode;
return hnode;
}
struct node *ptr=reverse_ll(hnode->next);
ptr->next=hnode;
hnode->next = NULL;
return hnode;
}
void display() {
if(!head) {
printf("empty");
return;
}
for(struct node *ptr = head; ptr; ptr = ptr->next) {
printf("%d->",ptr->data);
}
printf("null\n");
}
int main() {
for(int i = 1; i <= 5; i++) {
lastinsert(i);
}
display();
reverse_ll(head);
display();
// It's good practice to implement a function that frees you list
// which you would call here.
return 0;
}
和示例運行:
$ ./a.out
1->2->3->4->5->null
5->4->3->2->1->null
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