Merge pull request #8 from azizkayumov/access

Access

src/access.rs

@@ -0,0 +1,70 @@
+use crate::{
+    node::{Node, Parent},
+    splay::splay,
+};
+
+// constructs a path from the root to the node at idx
+pub fn access(forest: &mut Vec<Node>, node_idx: usize) {
+    splay(forest, node_idx);
+
+    if let Some(right_idx) = forest[node_idx].right {
+        forest[node_idx].right = None;
+        forest[right_idx].parent = Parent::Path(node_idx);
+    }
+
+    while let Parent::Path(path_idx) = forest[node_idx].parent {
+        splay(forest, path_idx);
+        // detach the right child of the path parent
+        if let Some(right_idx) = forest[path_idx].right {
+            forest[right_idx].parent = Parent::Path(path_idx);
+            forest[path_idx].right = None;
+        }
+
+        // attach the node as the path parent's right child
+        forest[path_idx].right = Some(node_idx);
+        forest[node_idx].parent = Parent::Node(path_idx);
+        splay(forest, node_idx);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::node::{Node, Parent};
+
+    fn create_nodes(n: usize) -> Vec<Node> {
+        (0..n).map(|i| Node::new(i, 0.0)).collect()
+    }
+
+    #[test]
+    pub fn access_base_case() {
+        // access a single node, should do nothing
+        let mut forest = create_nodes(1);
+        super::access(&mut forest, 0);
+        assert!(matches!(forest[0].parent, Parent::Root));
+    }
+
+    #[test]
+    pub fn access_splay_leaf() {
+        let mut forest = create_nodes(3);
+        // '1' has a path pointer to '0', '1' has a right child '2'.
+        // after access(2), '2' should be the root of the tree:
+        //    0             0             0               2
+        //    |             |              \             /
+        //    1      =>     2      =>       2     =>    0
+        //     \           /               /             \
+        //      2         1               1               1
+        forest[1].parent = Parent::Path(0);
+        forest[1].right = Some(2);
+        forest[2].parent = Parent::Node(1);
+        super::access(&mut forest, 2);
+        assert!(matches!(forest[2].parent, Parent::Root));
+        assert_eq!(forest[2].right, None);
+        assert_eq!(forest[2].left, Some(0));
+        assert!(matches!(forest[0].parent, Parent::Node(2)));
+        assert_eq!(forest[0].left, None);
+        assert_eq!(forest[0].right, Some(1));
+        assert!(matches!(forest[1].parent, Parent::Node(0)));
+        assert_eq!(forest[1].left, None);
+        assert_eq!(forest[1].right, None);
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
 #![allow(dead_code, clippy::module_name_repetitions)] // yes, I want to name my structs with the same name as the file
+mod access;
 mod node;
 mod splay;

src/splay.rs

@@ -1,6 +1,6 @@
 use crate::node::{Node, Parent};
 
-pub fn rotate_left(forest: &mut Vec<Node>, node_idx: usize) {
+fn rotate_left(forest: &mut Vec<Node>, node_idx: usize) {
     // base cases:
     // - node_idx is out of bounds
     // - node_idx should have a right child
@@ -27,7 +27,7 @@ pub fn rotate_left(forest: &mut Vec<Node>, node_idx: usize) {
     }
 }
 
-pub fn rotate_right(forest: &mut Vec<Node>, node_idx: usize) {
+fn rotate_right(forest: &mut Vec<Node>, node_idx: usize) {
     // base cases:
     // - node_idx is out of bounds
     // - node_idx should have a left child
@@ -118,8 +118,9 @@ mod tests {
         forest[0].right = Some(1);
         forest[1].parent = node::Parent::Node(0);
         rotate_left(&mut forest, 0);
-        assert_eq!(forest[0].right, None);
         assert_eq!(forest[1].left, Some(0));
+        assert_eq!(forest[0].right, None);
+        assert_eq!(forest[0].left, None);
         assert!(matches!(forest[0].parent, node::Parent::Node(1)));
         assert!(matches!(forest[1].parent, node::Parent::Root));
     }
@@ -233,7 +234,9 @@ mod tests {
         forest[1].parent = node::Parent::Node(0);
         super::splay(&mut forest, 1);
         assert_eq!(forest[0].right, None);
+        assert_eq!(forest[0].left, None);
         assert_eq!(forest[1].left, Some(0));
+        assert_eq!(forest[1].right, None);
         assert!(matches!(forest[0].parent, node::Parent::Node(1)));
         assert!(matches!(forest[1].parent, node::Parent::Root));
     }