Merge pull request #9 from azizkayumov/connected

Connected

src/access.rs

@@ -5,6 +5,7 @@ use crate::{
 
 // constructs a path from the root to the node at idx
 pub fn access(forest: &mut Vec<Node>, node_idx: usize) {
+    assert!(node_idx < forest.len(), "access: node_idx out of bounds");
     splay(forest, node_idx);
 
     if let Some(right_idx) = forest[node_idx].right {
@@ -36,15 +37,15 @@ mod tests {
     }
 
     #[test]
-    pub fn access_base_case() {
+    pub fn 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() {
+    pub fn access_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:

src/connected.rs

@@ -0,0 +1,71 @@
+use crate::{
+    access::access,
+    node::{Node, Parent},
+};
+
+pub fn connected(forest: &mut Vec<Node>, v: usize, w: usize) -> bool {
+    assert!(
+        v < forest.len() || w < forest.len(),
+        "splay: node_idx out of bounds"
+    );
+    access(forest, v); // v is now the root of the tree
+    access(forest, w);
+    // if v is not the root of the tree anymore, then v and w are connected:
+    !matches!(forest[v].parent, Parent::Root) || v == w
+}
+
+#[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 base_case() {
+        // check two nodes, should return false
+        let mut forest = create_nodes(2);
+        assert!(!super::connected(&mut forest, 0, 1));
+    }
+
+    #[test]
+    pub fn connected_with_root() {
+        // check three nodes, one is root:
+        //    0
+        //   / \
+        //  1   2
+        let mut forest = create_nodes(3);
+        forest[0].left = Some(1);
+        forest[0].right = Some(2);
+        forest[1].parent = Parent::Node(0);
+        forest[2].parent = Parent::Node(0);
+
+        assert!(super::connected(&mut forest, 0, 1));
+        assert!(super::connected(&mut forest, 0, 2));
+        assert!(super::connected(&mut forest, 1, 2));
+        assert!(super::connected(&mut forest, 0, 0));
+        assert!(super::connected(&mut forest, 1, 1));
+        assert!(super::connected(&mut forest, 2, 2));
+    }
+
+    #[test]
+    pub fn connected_with_path_pointers() {
+        // check two trees that are connected by a path pointer
+        //     0
+        //    / \
+        //   1   2
+        //       |
+        //       3
+        let mut forest = create_nodes(4);
+        forest[0].left = Some(1);
+        forest[0].right = Some(2);
+        forest[1].parent = Parent::Node(0);
+        forest[2].parent = Parent::Node(0);
+        forest[3].parent = Parent::Path(2);
+
+        assert!(super::connected(&mut forest, 0, 3));
+        assert!(super::connected(&mut forest, 1, 3));
+        assert!(super::connected(&mut forest, 2, 3));
+    }
+}

src/lib.rs

@@ -1,4 +1,5 @@
 #![allow(dead_code, clippy::module_name_repetitions)] // yes, I want to name my structs with the same name as the file
 mod access;
+mod connected;
 mod node;
 mod splay;