doublelinlist

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

typedef struct node{
    int n;
    struct node *prev, *next;
}node_t;

node_t headnode, tailnode = {0, &headnode, NULL};
node_t *head = &headnode, *tail = &tailnode;

node_t *mk_node(int n)
{
    node_t *p = malloc(sizeof(node_t));
    if(p){
        p->n = n;
        p->prev = p->next = NULL;
    }
    return p;
}

void insert_head(int n)
{
    node_t *newp = mk_node(n);

    if(newp){
        newp->prev = head;
        newp->next = head->next;
        head->next->prev = newp;
        head->next = newp;
    }
}

void insert_tail(int n)
{
    node_t *newp = mk_node(n);

    if(newp){
        newp->prev = tail->prev;
        newp->next = tail;
        tail->prev->next = newp;
        tail->prev = newp;
    }
}

void insert_seq(int n)
{
    node_t *newp = mk_node(n);
    node_t *cur;

    if(newp){
        for(cur = head->next; cur != tail && cur->n < n; cur = cur->next)
            ;
        newp->prev = cur->prev;
        newp->next = cur;
        cur->prev->next = newp;
        cur->prev = newp;
    }
}

node_t *del_node(int n)
{
    node_t *del, *cur;

    for(cur = head->next; cur != tail; cur = cur->next){
        if(cur->n == n){
            del = cur;
            cur->prev->next = cur->next;
            cur->next->prev = cur->prev;
            del->prev = del->next = NULL;
            return del;
        }
    }
    return NULL;
}

void disp_node(void)
{
    node_t *cur;

    printf("disp...\n");
    for(cur = head; cur != tail; cur = cur->next){
        printf("%d\n", cur->n);
    }
}

void destroy_linklist(void)
{
    node_t *cur, *next;

    printf("disp...\n");
    for(cur = head->next; cur != tail; cur = next){
        next = cur->next;
        free(cur);    
    }
}

int main(void)
{
    int n;
    node_t *del;
    headnode.next = &tailnode;

    while(1){
        scanf("%d", &n);
        if(!n)
            break;
        insert_seq(n);
    }
    disp_node();
    while((del = del_node(3))){
        printf("del:%d\n", del->n);
        free(del);
    }
    disp_node();
    destroy_linklist();

    return 0;
}