tree/src/lib.rs

@@ -9,6 +9,10 @@ use std::{
     rc::Rc,
 };
 
+// I need to take what I learned about linked lists and about the other Tree data structure, and
+// apply it here with arena allocation.
+//
+// Also, smarter node allocation and pointer handling in order to avoid clones.
 #[derive(Clone, Debug, Default)]
 pub enum Tree<T> {
     #[default]
@@ -55,6 +59,16 @@ impl<T> Tree<T> {
         None
     }
 
+    // Do a depth-first-search in order to get the path to a node. Start with a naive recursive
+    // implementation, then switch to a stack-based implementation in order to avoid exceeding the
+    // stack.
+    pub fn path_to<F>(&self, f: F) -> Vec<Node<T>>
+    where
+        F: FnOnce(&T) -> bool + Copy,
+    {
+        unimplemented!()
+    }
+
     /// Convert each node of a tree from type T to type U
     pub fn map<F, U>(&self, op: F) -> Tree<U>
     where
@@ -146,6 +160,13 @@ impl<T> Node<T> {
     }
 }
 
+impl<T: PartialEq> PartialEq for Node<T> {
+    fn eq(&self, other: &Node<T>) -> bool {
+        self.0.borrow().value == other.0.borrow().value
+            && self.0.borrow().children == other.0.borrow().children
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -184,4 +205,31 @@ mod tests {
         assert!(tree2.find_bfs(|val| *val == "16").is_some());
         assert!(tree2.find_bfs(|val| *val == "17").is_some());
     }
+
+    #[test]
+    fn path_to_on_empty_tree_returns_empty() {
+        let tree: Tree<&str> = Tree::default();
+
+        assert_eq!(tree.path_to(|val| *val == "i"), vec![]);
+    }
+
+    // A
+    // B G   H
+    // C     I
+    // D E F
+    #[test]
+    fn it_can_find_a_path_to_a_node() {
+        let (tree, a) = Tree::new("A");
+        let b = a.add_child_value("B");
+        let c = b.add_child_value("C");
+        let _d = c.add_child_value("D");
+        let _e = c.add_child_value("D");
+        let _f = c.add_child_value("D");
+        let _g = a.add_child_value("G");
+        let h = a.add_child_value("H");
+        let i = a.add_child_value("I");
+
+        assert_eq!(tree.path_to(|val| *val == "z"), vec![]);
+        assert_eq!(tree.path_to(|val| *val == "i"), vec![a, h, i]);
+    }
 }