data_structures_and_algorithms/doubly_linked_lists/insertion.c at main · mdawoud27/data_structures_and_algorithms · GitHub

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#include "linked_list.h"

node *insert_first(node *head, int value)
{
	node *new = malloc(sizeof(node));
	new->value = value;
	new->next = NULL;

	if (!head)
		new->prev = NULL;

	else
	{
		new->next = head;
		head->prev = new;
	}

	head = new;
	return head;
}

node *insert_end(node *head, int value)
{
	node *new = malloc(sizeof(node)), *ptr = NULL;
	new->value = value;
	new->next = NULL;

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

	ptr = head;
	while (ptr->next)
		ptr = ptr->next;

	ptr->next = new;
	new->prev = ptr;

	return head;
}

node *insert_pos(node *head, int value, int pos)
{
	node *new = malloc(sizeof(node)), *ptr = NULL;

	if (!new)
	{
		printf("Memory allocation failed\n");
		return head;
	}

	new->value = value;
	new->next = NULL;

	if (pos == 0)
	{
		if (!head)
			new->prev = NULL;

		else
		{
			new->next = head;
			head->prev = new;
		}

		head = new;
		return head;
	}

	else if (pos == count_nodes(head))
	{
		if (!head)
		{
			new->prev = NULL;
			head = new;
			return head;
		}

		ptr = head;
		while (ptr->next)
			ptr = ptr->next;

		ptr->next = new;
		new->prev = ptr;

		return head;
	}

	else
	{
		ptr = head;
		for (int i = 0; i < pos - 1; i++)
			ptr = ptr->next;

		node *temp = ptr;
		new->next = temp->next;
		new->prev = ptr;
		ptr->next = new;

		return head;
	}
}