더블링크드 리스트 c 언어

학교 수업때 한거

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
 
typedef int element;
 
typedef struct ListNode {
    element data;
    struct ListNode *rlink;
    struct ListNode *llink;
} ListNode;
 
void insert_node(ListNode *before, ListNode *new_node)
{
    new_node->llink = before;
    new_node->rlink = before->rlink;
    before->rlink->llink = new_node;
    before->rlink = new_node;
}
 
void display_r(ListNode *head)
{
    ListNode *p = head;
    p = head->rlink;
    while (p != head) {
        printf("%d->", p->data);
        p = p->rlink;
    }
    printf("\n");
}
 
 
void display_l(ListNode *tail)
{
    ListNode *p = tail;
    ListNode *q = tail;
 
    while (p->llink != q) {
        printf("%d->", p->data);
        p = p->llink;
    }
    printf("\n");
}
 
void main() {
 
    ListNode * head;
    head = (ListNode*)malloc(sizeof(ListNode));
    head->llink = head;
    head->rlink = head;
 
    ListNode * p1;
    p1 = (ListNode*)malloc(sizeof(ListNode));
    p1->data = 1;
    insert_node(head, p1);
    //display_r(head);
 
    ListNode * p2;
    p2 = (ListNode*)malloc(sizeof(ListNode));
    p2->data = 3;
    insert_node(p1, p2);
 
    ListNode * p3;
    p3 = (ListNode*)malloc(sizeof(ListNode));
    p3->data = 5;
 
    insert_node(p2, p3);
 
    display_r(head);
    display_l(p3);
}