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

typedef int element_t;

struct list {
  struct node {
    struct node *next, *previous;
    element_t e;
  } * head, *tail;
};

void list_init(struct list *l) { l->head = l->tail = NULL; }

struct node *list_add_back(struct list *l, element_t e) {
  struct node *newNode = malloc(sizeof(struct node));
  newNode->next = 0;
  newNode->e = e;
  if (l->tail == NULL) {
    newNode->previous = NULL;
    l->head = l->tail = newNode;
  } else {
    newNode->previous = l->tail;
    l->tail->next = newNode;
    l->tail = newNode;
  }
  return newNode;
}

void list_delete_node(struct list *l, struct node *n) {
  if (n->previous == NULL)
    l->head = n->next;
  else
    n->previous->next = n->next;
  if (n->next == NULL)
    l->tail = n->previous;
  else
    n->next->previous = n->previous;
  free(n);
}

void list_delete_value(struct list *l, element_t e) {
  struct node *n = l->head, *next;
  while (n != NULL) {
    next = n->next;
    if (n->e == e)
      list_delete_node(l, n);
    n = next;
  }
}

void list_print(struct list *l, int reverse) {
  struct node *n = reverse ? l->tail : l->head;
  while (n != NULL) {
    printf("%d\n", n->e);
    n = reverse ? n->previous : n->next;
  }
}

void *adder(void *arg) {
  struct list *l = (struct list *)arg;
  srand(time(0));
  while (1) {
    list_add_back(l, rand() % 25);
    usleep(10);
  }
}

void *remover(void *arg) {
  struct list *l = (struct list *)arg;
  srand(time(0) + 2);
  while (1) {
    list_delete_value(l, rand() % 25);
    usleep(5);
  }
}

int main() {
  struct list l;
  list_init(&l);
  
  pthread_t a, r;
  pthread_create(&a, NULL, adder, &l);
  pthread_create(&r, NULL, remover, &l);
  pthread_detach(a);
  pthread_detach(r);

  while (getchar() != EOF)
    list_print(&l, 0);
  return 0;
}