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

typedef struct Student student;
struct Student {
  int sid;
  struct Student *next;
};

void insert(student **head, int idx, uint sid) {
  student *new = malloc(sizeof(student));
  new->sid = sid;

  int i = 0;

  student *prev = NULL, *cur = *head;

  for (int i = 0;; i++) {
    if (i == idx) {
      if (prev != NULL)
        prev->next = new;
      else
        *head = new;
      new->next = cur;
      return;
    }

    if (cur == NULL)
      return;

    prev = cur;
    cur = cur->next;
  }

  printf("Index %d does not exist\n", idx);
  return;
}

void delete (student **head, int idx) {
  student *prev = NULL, *cur = *head;

  for (int i = 0; cur != NULL; i++) {
    if (i == idx) {
      if (prev != NULL)
        prev->next = cur->next;
      else
        *head = cur->next;
      free(cur);
      return;
    }
    prev = cur;
    cur = cur->next;
  }

  printf("Index %d does not exist\n", idx);
  return;
}

void reverse(student **head) {
  student *prev = NULL, *cur = *head;

  while (cur->next != NULL) {
    student *next = cur->next;
    cur->next = prev;
    prev = cur;
    cur = next;
  }

  cur->next = prev;

  *head = cur;
  return;
}

int main() {
  student *head = NULL;
  insert(&head, 0, 1);
  insert(&head, 1, 2002);
  insert(&head, 2, -9);
  insert(&head, 3, 52);
  insert(&head, 1, 4);
  delete (&head, 2);
  reverse(&head);

  while (head != NULL) {
    printf("%d ", head->sid);
    head = head->next;
  }

  // free
  while (head != NULL)
    delete(&head, 0);
}