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

typedef struct node {
  int val;
  struct node *next;
} NODE;

NODE *init_node(int val) {
  NODE *buf;
  buf = malloc(sizeof(NODE));
  if (buf == NULL) {
    fprintf(stderr, "Error allocating node\n");
    return NULL;
  }
  buf->val = val;
  buf->next = NULL;
  return buf;
}

void add_node(NODE *list, int val) {
  NODE *node = init_node(val);
  if (node == NULL) {
    return;
  }
  for (; list->next != NULL; list = list->next);
  list->next = node;
}

void del_node(NODE *list, NODE *node) {
  for (; list->next != NULL; list = list->next) {
    if (list->next == node) {
      list->next = (list->next)->next;
      free(node);
      return;
    }
  }
}

int count_length(NODE *list) {
  int counter = 1;
  for (; list->next != NULL; list = list->next) {
    counter++;
  }
  return counter;
}

void print_list(NODE *list) {
  for (; list->next != NULL; list = list->next) {
    printf("%d\n", list->val);
  }
  printf("%d\n", list->val);
}

NODE *reverse_list(NODE *list) {
  NODE *prev = NULL;
  NODE *next = list->next;
  while (next != NULL) {
    list->next = prev;
    prev = list;
    list = next;
    next = list->next;
  }
  list->next = prev;
  return list;
}

void delete_list(NODE* list) {
  if(list -> next == NULL) {
    free(list);
    return;
  }
  NODE* next_node = list -> next;
  while (next_node != NULL) {
    free(list);
    list = next_node;
    next_node = list -> next;
  }
  free(list);
  return;
}

NODE* list_remove_all(NODE *list, int val) {
  NODE* head = list;
  NODE* buf;
  while (head != NULL && head->val == val) {
    buf = head->next;
    free(head);
    head = buf;
  }
  if (head == NULL) return head;
  list = head;
  while (list->next != NULL) {
    if (list->next->val == val) {
      while(list->next != NULL && list->next->val == val) {
        buf = list->next;
        list->next = list->next->next;
        free(buf);
      }
    } else list = list->next;
  }
  return head;
}

int main() {
  NODE *list = init_node(4);
  add_node(list, 5);
  print_list(list);
  printf("\n[%d]\n\n", count_length(list));
  del_node(list, list->next);
  print_list(list);
  printf("\n[%d]\n\n", count_length(list));
  add_node(list, 1);
  add_node(list, 2);
  add_node(list, 3);
  add_node(list, 4);
  add_node(list, 3);
  add_node(list, 3);
  add_node(list, 1);
  print_list(list);
  printf("\n[%d]\n\n", count_length(list));
  list = reverse_list(list);
  print_list(list);
  printf("\n[%d]\n\n", count_length(list));
  list = list_remove_all(list, 1);
  print_list(list);
  printf("\n[%d]\n\n", count_length(list));
  delete_list(list);
  return 0;
}