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use super::{DoublyLinkedList, ListNode};
impl<T> DoublyLinkedList<T> {
/// Inserts an item of type `T` at the start of the `DoublyLinkedList`
///
/// # Parameters
/// - `data`: The new value to be inserted.
///
/// # Examples
/// ```
/// use villa01_data_structures::doubly_linked_list::DoublyLinkedList;
///
/// let mut list: DoublyLinkedList<i32> = DoublyLinkedList::new();
/// list.insert_at_beginning(1);
/// assert_eq!(list.len(), 1);
/// ```
pub fn insert_at_beginning(&mut self, data: T) {
let new_node = Box::into_raw(Box::new(ListNode::new(data)));
match self.head {
Some(head) => {
unsafe {
(*new_node).next = Some(head);
(*head).prev = Some(new_node);
}
self.head = Some(new_node);
}
None => {
// The list is empty and should be initialized
self.head = Some(new_node);
self.tail = Some(new_node);
}
}
self.length += 1;
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_empty_list() {
let mut list: DoublyLinkedList<i32> = DoublyLinkedList::new();
list.insert_at_beginning(1);
assert!(!list.is_empty());
assert_eq!(list.len(), 1);
}
#[test]
fn test_existing_head() {
let mut list: DoublyLinkedList<i32> = DoublyLinkedList::with_value(2);
list.insert_at_beginning(1);
assert_eq!(list.len(), 2);
}
#[test]
fn test_with_several_nodes() {
struct T {}
let mut list: DoublyLinkedList<T> = DoublyLinkedList::new();
let list_length: usize = 100;
for _ in 1..list_length + 1 {
list.insert_at_beginning(T {});
}
assert_eq!(list.len(), list_length);
}
}