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use std::rc::Rc;
#[derive(Debug, Clone, Default, PartialEq, Eq)]
struct Node<T> {
val: T,
next: Option<Rc<Node<T>>>,
}
#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub(crate) struct Stack<T> {
head: Option<Rc<Node<T>>>,
}
impl<T> Stack<T> {
pub(crate) fn new() -> Self {
Self { head: None }
}
pub(crate) fn peek(&self) -> Option<&T> {
self.head.as_deref().map(|n| &n.val)
}
pub(crate) fn pop(&self) -> Option<Stack<T>> {
self.head.as_deref().map(|n| Self {
head: n.next.clone(),
})
}
pub(crate) fn push(&self, v: T) -> Stack<T> {
Self {
head: Some(Rc::new(Node {
val: v,
next: self.head.clone(),
})),
}
}
pub(crate) fn size(&self) -> usize {
let mut count = 0;
let mut node = &self.head;
while let Some(next) = node {
count += 1;
node = &next.next;
}
count
}
pub(crate) fn is_empty(&self) -> bool {
self.head.is_none()
}
}