node operations

src/lib.rs

@@ -1 +1,2 @@
+/// A doubly linked list
 pub mod linked_list;

src/linked_list.rs

@@ -2,55 +2,113 @@ use std::fmt::{Debug, Formatter};
 use std::marker::PhantomData;
 use std::ptr::NonNull;
 
-/// A doubly linked list with unsafe :O, except it's kind of shit compared to the std one
+/// A doubly linked list using unsafe code.  
+/// It is loosely inspired by the `std::collections::LinkedList`, but I haven't looked at that one too close,
+/// so most it is my own.
+///
+/// It was not made with efficiency in mind, but at least it doesn't but `std::rc::Rc` everywhere, but uses
+/// unsafe pointers instead.
+///
+/// # How to use
+/// ```
+/// use datastructures::linked_list::LinkedList;
+///
+/// let mut list = LinkedList::new();
+/// list.push_front("hello");
+/// assert_eq!(list.get(0), Some(&"hello"));
+/// list.push_end("bye");
+/// assert_eq!(list.get(1), Some(&"bye"));
+/// ```
+///
+/// The list can also be edited using the `Node` methods
+/// ```
+/// use datastructures::linked_list::LinkedList;
+///
+/// let mut list = LinkedList::new();
+/// list.push_front(1);
+/// let mut node = list.get_head_node_mut().unwrap();
+/// node.push_after(3);
+/// node.push_after(2);
+/// let next = node.get_next().unwrap();
+/// let next = next.get_next().unwrap();
+/// assert_eq!(*next.get_value(), 3);
+/// ```
+///
+/// # Note
+/// You should generally not use Linked Lists, and if you really do need to use one, use `std::collections::LinkedList`
 pub struct LinkedList<T> {
     start: Option<NonNull<Node<T>>>,
     end: Option<NonNull<Node<T>>>,
-    _maker: PhantomData<T>,
+    _marker: PhantomData<T>,
 }
 
 impl<T> LinkedList<T> {
     /// Creates a new empty Linked List
     pub fn new() -> LinkedList<T> {
-        std::collections::LinkedList::new().push_front("hi");
         Self {
             start: None,
             end: None,
-            _maker: PhantomData,
+            _marker: PhantomData,
         }
     }
 
-    /// Prepend an element to the start of the list
+    /// Push an element to the start of the list (O(1))
     pub fn push_front(&mut self, element: T) {
         match self.start {
             // empty list
             None => {
-                let node = allocate_nonnull(Node {
+                let new_node = allocate_nonnull(Node {
                     value: element,
                     next: None,
                     prev: None,
-                    _maker: PhantomData,
+                    _marker: PhantomData,
                 });
-                self.start = Some(node);
+                self.start = Some(new_node);
-                self.end = Some(node);
+                self.end = Some(new_node);
             }
             // at lest one element
-            Some(mut node) => {
+            Some(mut old_start) => {
-                let new = allocate_nonnull(Node {
+                let new_node = allocate_nonnull(Node {
                     value: element,
-                    next: Some(node),
+                    next: Some(old_start),
                     prev: None,
-                    _maker: PhantomData,
+                    _marker: PhantomData,
                 });
                 // SAFETY: All pointers should always be valid
-                unsafe { node.as_mut() }.prev = Some(new);
+                unsafe { old_start.as_mut() }.prev = Some(new_node);
-                self.start = Some(new);
+                self.start = Some(new_node);
             }
         }
     }
 
-    pub fn _insert_end(&mut self, _element: T) {}
+    /// Push an element to the end of the list (O(1))
+    pub fn push_end(&mut self, element: T) {
+        match self.end {
+            None => {
+                let new_node = allocate_nonnull(Node {
+                    value: element,
+                    next: None,
+                    prev: None,
+                    _marker: PhantomData,
+                });
+                self.start = Some(new_node);
+                self.end = Some(new_node);
+            }
+            Some(mut old_end) => {
+                let new_node = allocate_nonnull(Node {
+                    value: element,
+                    next: None,
+                    prev: Some(old_end),
+                    _marker: PhantomData,
+                });
+                // SAFETY: All pointers should always be valid
+                unsafe { old_end.as_mut() }.next = Some(new_node);
+                self.end = Some(new_node);
+            }
+        }
+    }
 
+    /// Get an element from the list (O(n))
     pub fn get(&self, mut index: usize) -> Option<&T> {
         let mut node = &self.start;
         let mut result = None;
@@ -67,7 +125,68 @@ impl<T> LinkedList<T> {
         result
     }
 
-    pub fn _get_node(&self, _index: usize) {}
+    /// Gets the last element from the list (O(1))
+    pub fn get_tail(&self) -> Option<&T> {
+        self.end.as_ref().map(|nn| unsafe { &nn.as_ref().value })
+    }
+
+    /// Gets the first element from the list (O(1))
+    pub fn get_head(&self) -> Option<&T> {
+        self.start.as_ref().map(|nn| unsafe { &nn.as_ref().value })
+    }
+
+    /// Get a node from the list that can only be used for navigation
+    pub fn get_node(&self, mut index: usize) -> Option<&Node<T>> {
+        let mut node = &self.start;
+        let mut result = None;
+        while let Some(content) = node {
+            // SAFETY: All pointers should always be valid
+            let content = unsafe { content.as_ref() };
+            if index == 0 {
+                result = Some(content);
+                break;
+            }
+            index -= 1;
+            node = &content.next;
+        }
+        result
+    }
+
+    /// Get the head node from the list that can only be used for navigation
+    pub fn get_head_node(&self) -> Option<&Node<T>> {
+        self.start.as_ref().map(|nn| unsafe { nn.as_ref() })
+    }
+
+    /// Get the tail node from the list that can only be used for navigation
+    pub fn get_tail_node(&self) -> Option<&Node<T>> {
+        self.end.as_ref().map(|nn| unsafe { nn.as_ref() })
+    }
+    /// Get the head node from the list that can be used the edit the list
+    pub fn get_head_node_mut(&mut self) -> Option<&mut Node<T>> {
+        self.start.as_mut().map(|nn| unsafe { nn.as_mut() })
+    }
+
+    /// Get the tail node from the list that can be used the edit the list
+    pub fn get_tail_node_mut(&mut self) -> Option<&mut Node<T>> {
+        self.end.as_mut().map(|nn| unsafe { nn.as_mut() })
+    }
+
+    /// Get a node from the list that can be used the edit the list
+    pub fn get_node_mut(&mut self, mut index: usize) -> Option<&mut Node<T>> {
+        let mut node = &mut self.start;
+        let mut result = None;
+        while let Some(ref mut content) = node {
+            // SAFETY: All pointers should always be valid
+            let content = unsafe { content.as_mut() };
+            if index == 0 {
+                result = Some(content);
+                break;
+            }
+            index -= 1;
+            node = &mut content.next;
+        }
+        result
+    }
 
     /// Returns an iterator over the items
     pub fn iter(&self) -> Iter<T> {
@@ -75,10 +194,7 @@ impl<T> LinkedList<T> {
     }
 }
 
-impl<T> Debug for LinkedList<T>
+impl<T: Debug> Debug for LinkedList<T> {
-where
-    T: Debug,
-{
     fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
         f.debug_list().entries(self.iter()).finish()
     }
@@ -104,12 +220,102 @@ impl<T> Drop for LinkedList<T> {
 }
 
 /// A Node in a `LinkedList`
+/// Can be used to navigate the `LinkedList`, using the `Node::get_next` and `Node::get_previous` methods,
+/// and edit the List using the push methods.
+///
+/// # Examples
+/// ```
+/// use datastructures::linked_list::*;
+///
+/// let mut list = LinkedList::new();
+/// list.push_front(1);
+/// let mut node = list.get_node_mut(0);
+/// ```
+///
 #[derive(Debug)]
 pub struct Node<T> {
     value: T,
     next: Option<NonNull<Node<T>>>,
     prev: Option<NonNull<Node<T>>>,
-    _maker: PhantomData<T>,
+    _marker: PhantomData<T>,
+}
+
+impl<T> Node<T> {
+    /// Push a value after this node
+    pub fn push_after(&mut self, element: T) {
+        let new_node = Some(allocate_nonnull(Node {
+            value: element,
+            next: self.next,
+            prev: NonNull::new(self as _),
+            _marker: PhantomData,
+        }));
+        self.next.map(|mut next| {
+            // SAFETY: All pointers should always be valid and created from a box
+            unsafe { next.as_mut() }.prev = new_node
+        });
+        self.next = new_node;
+    }
+
+    /// Push a value before this node
+    pub fn push_before(&mut self, element: T) {
+        let new_node = Some(allocate_nonnull(Node {
+            value: element,
+            next: NonNull::new(self as _),
+            prev: self.prev,
+            _marker: PhantomData,
+        }));
+        self.prev.map(|mut next| {
+            // SAFETY: All pointers should always be valid and created from a box
+            unsafe { next.as_mut() }.next = new_node
+        });
+        self.prev = new_node;
+    }
+
+    /// Get the next node
+    pub fn get_next(&self) -> Option<&Node<T>> {
+        match &self.next {
+            None => None,
+            Some(nn) => unsafe { Some(nn.as_ref()) },
+        }
+    }
+    /// Get the next node mutably
+    pub fn get_next_mut(&mut self) -> Option<&mut Node<T>> {
+        match &mut self.next {
+            None => None,
+            Some(nn) => unsafe { Some(nn.as_mut()) },
+        }
+    }
+
+    /// Get the previous node
+    pub fn get_previous(&self) -> Option<&Node<T>> {
+        match &self.prev {
+            None => None,
+            Some(nn) => unsafe { Some(nn.as_ref()) },
+        }
+    }
+
+    /// Get the previous node mutably
+    pub fn get_previous_mut(&mut self) -> Option<&mut Node<T>> {
+        match &mut self.prev {
+            None => None,
+            Some(nn) => unsafe { Some(nn.as_mut()) },
+        }
+    }
+
+    /// Gets the value from the node
+    pub fn get_value(&self) -> &T {
+        &self.value
+    }
+
+    /// Gets the value from the node
+    pub fn set_value(&mut self, value: T) {
+        self.value = value;
+    }
+
+    /// Gets the value from the node and replaces it with the old one
+    pub fn replace_value(&mut self, value: T) -> T {
+        std::mem::replace(&mut self.value, value)
+    }
 }
 
 fn allocate_nonnull<T>(element: T) -> NonNull<T> {
@@ -118,6 +324,7 @@ fn allocate_nonnull<T>(element: T) -> NonNull<T> {
     unsafe { NonNull::new_unchecked(Box::leak(boxed)) }
 }
 
+/// The iterator over the linked list
 pub struct Iter<'a, T> {
     item: Option<&'a Node<T>>,
 }
@@ -133,7 +340,7 @@ impl<'a, T> Iter<'a, T> {
     }
 }
 
-impl<'a, T: Debug> Iterator for Iter<'a, T> {
+impl<'a, T> Iterator for Iter<'a, T> {
     type Item = &'a T;
 
     fn next(&mut self) -> Option<Self::Item> {
@@ -167,6 +374,18 @@ mod test {
         assert_eq!(list.get(3), None);
     }
 
+    #[test]
+    fn push_start_end() {
+        let mut list = LinkedList::new();
+        list.push_end(3);
+        list.push_front(2);
+        list.push_front(1);
+        list.push_end(4);
+        list.push_end(5);
+        let vec = list.iter().cloned().collect::<Vec<_>>();
+        assert_eq!(&vec[..], &[1, 2, 3, 4, 5]);
+    }
+
     #[test]
     fn iter_simple() {
         let mut list = LinkedList::new();
@@ -202,4 +421,35 @@ mod test {
         }
         assert_eq!(list.get(999999), Some(&0));
     }
+
+    #[test]
+    fn node_operations() {
+        let mut list = LinkedList::new();
+        list.push_front(1);
+        list.push_end(2);
+        {
+            let node = list.get_node_mut(1).unwrap();
+            assert_eq!(*node.get_value(), 2);
+            node.push_after(4);
+            let next = node.get_next_mut().unwrap();
+            assert!(matches!(next.get_next(), None));
+            next.push_before(3)
+        }
+        let vec = list.iter().cloned().collect::<Vec<_>>();
+        assert_eq!(&vec[..], &[1, 2, 3, 4]);
+    }
+
+    #[test]
+    fn node_values() {
+        let mut list = LinkedList::new();
+        list.push_front(1);
+        let node = list.get_node_mut(0).unwrap();
+        assert_eq!(*node.get_value(), 1);
+        assert_eq!(node.replace_value(2), 1);
+        assert_eq!(*node.get_value(), 2);
+        node.push_after(3);
+        let node = node.get_next_mut().unwrap();
+        node.set_value(4);
+        assert_eq!(*node.get_value(), 4);
+    }
 }