Add backtrack function.

src/lib.rs

@@ -12,6 +12,7 @@
 extern crate alloc;
 mod node;
 
+use alloc::collections::vec_deque::VecDeque;
 use alloc::string::{String, ToString};
 use alloc::vec;
 use alloc::vec::Vec;
@@ -58,7 +59,7 @@ impl<NodeValueT: NodeValue> Graph<NodeValueT> {
             node.set_value(value);
             return Ok(());
         }
-        return Err(GraphError::from_msg("Can't set value of invalid key."));
+        Err(GraphError::from_msg("Can't set value of invalid key."))
     }
 
     /// Get the value of key `key` if the key is valid.
@@ -104,7 +105,7 @@ impl<NodeValueT: NodeValue> Graph<NodeValueT> {
             }
         }
 
-        return Ok(leaf_keys);
+        Ok(leaf_keys)
     }
 
     /// Return all keys ordered like you were doing
@@ -126,6 +127,22 @@ impl<NodeValueT: NodeValue> Graph<NodeValueT> {
 
         Ok(visited_keys)
     }
+
+    /// Given a key, return the vec of keys connecting that key to the root.
+    /// Order is root->key inclusive.
+    pub fn backtrack_from_key(&self, key: &Key) -> Result<Vec<Key>, GraphError> {
+        let mut curr_key = key.clone();
+        let mut deque = VecDeque::<Key>::new();
+        deque.push_front(curr_key.clone());
+
+        while curr_key != self.root_key() {
+            let new_parent = self.parent_of(&curr_key)?.unwrap();
+            deque.push_front(new_parent.clone());
+            curr_key = new_parent;
+        }
+
+        Ok(Vec::from(deque))
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -193,6 +210,7 @@ mod tests {
 
     #[test]
     fn graph_search() {
+        // Build the graph.
         let root_val = NodeType::new(1.0);
         let mut graph = Graph::new(root_val);
 
@@ -212,11 +230,16 @@ mod tests {
         let fifth_add_res = graph.add(fifth_val, 2);
         assert!(fifth_add_res.is_ok());
 
+        // Do the testing.
         let leaf_keys = graph.find_leaf_keys().unwrap();
         assert!(leaf_keys.len() == 2);
 
         let keys_by_depth = graph.get_keys_by_depth().unwrap();
         let expected_keys_by_depth = vec![0, 2, 4, 1, 3];
         assert!(keys_by_depth == expected_keys_by_depth);
+
+        let backtracked_keys = graph.backtrack_from_key(&4).unwrap();
+        let expected_backtracked_keys = vec![0, 2, 4];
+        assert!(backtracked_keys == expected_backtracked_keys);
     }
 }