doubly-linkedlist-double-pointer-operations.c

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

typedef struct Node {
  int data;
  struct Node *next;
  struct Node *prev;
} Node;

void insert_end(Node **head, int data);
void insert_begin(Node **head, int data);
void delete_end(Node **head);
void delete_begin(Node **head);
Node* find(Node *head, int data);
void display(Node *head);

int main() {
  Node *head = NULL;

  insert_end(&head, 1);
  insert_end(&head, 2);
  insert_end(&head, 3);

  display(head);

  insert_begin(&head, 7);
  insert_begin(&head, 8);
  insert_begin(&head, 9);

  display(head);

  delete_begin(&head);
  delete_begin(&head);

  display(head);

  delete_end(&head);
  delete_end(&head);
  display(head);
  
  return 0;
}

void insert_end(Node **head, int data) {
  Node *new = (Node*)malloc(sizeof(Node));
  new->data = data;
  new->next = NULL;

  if (*head == NULL) {
    new->prev = NULL;
    *head = new;
    return;
  }

  Node *curr = *head;
  while (curr->next != NULL) curr = curr->next;

  new->prev = curr;
  curr->next = new;
}

void insert_begin(Node **head, int data) {
  Node *new = (Node*)malloc(sizeof(Node));
  new->data = data;
  new->next = *head;
  new->prev = NULL;

  *head = new;
}

void delete_begin(Node **head) {
  if (*head == NULL) return;
  Node *t = *head;
  *head = (*head)->next;
  free(t);
}

void delete_end(Node **head) {
  if (*head == NULL) return;

  Node *curr = *head;
  while (curr->next != NULL) curr = curr->next;
  Node *prev = curr->prev;

  if (prev == NULL) *head = NULL;
  else prev->next = NULL;

  free(curr);
}

Node* find(Node *head, int data) {
  while (head != NULL) {
    if (head->data == data) {
      return head;
    }

    head = head->next;
  }

  return NULL;
}

void display(Node *head) {
  while (head != NULL) {
    printf("%d ", head->data);
    head = head->next;
  }

  printf("\n");
}