diff --git a/src/euler31/Cargo.toml b/src/euler31/Cargo.toml
new file mode 100644
index 0000000..b83af93
--- /dev/null
+++ b/src/euler31/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "euler31"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/src/euler31/src/main.rs b/src/euler31/src/main.rs
new file mode 100644
index 0000000..c8d17ce
--- /dev/null
+++ b/src/euler31/src/main.rs
@@ -0,0 +1,94 @@
+#![allow(dead_code)]
+use std::ops::Index;
+
+const VALUE: u8 = 200;
+
+type Values = Vec<u8>;
+
+fn main() {
+    // let head = Tree::new(200);
+}
+
+#[derive(Debug, PartialEq)]
+struct Node {
+    values: Values,
+    nodes: Vec<Node>,
+}
+
+impl Node {
+    fn new(value: u8) -> Self {
+        Self {
+            values: vec![value],
+            nodes: vec![],
+        }
+    }
+
+    fn new_vec(values: Values) -> Self {
+        Self {
+            values,
+            nodes: vec![],
+        }
+    }
+
+    fn iter(&mut self) {
+        if !self.nodes.is_empty() {
+            self.nodes.iter_mut().for_each(|n| n.iter())
+        } else {
+            let mut previous: Option<Values> = None;
+            for (i, value) in self.values.iter().enumerate() {
+                let j = i * 2;
+                let half = value / 2;
+                let mut new_vec;
+                if let Some(inner) = previous {
+                    new_vec = inner.clone();
+                } else {
+                    new_vec = self.values.clone();
+                };
+
+                new_vec[j] = half;
+                new_vec.insert(j, half);
+                previous = Some(new_vec.clone());
+                debug_assert_eq!(new_vec.iter().sum::<u8>(), VALUE);
+                self.nodes.push(Node::new_vec(new_vec));
+            }
+        }
+    }
+}
+
+impl Index<usize> for Node {
+    type Output = Node;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.nodes[index]
+    }
+}
+
+#[cfg(test)]
+mod test {
+    // use crate::Node;
+    use crate::Node;
+
+    #[test]
+    fn test_new() {
+        let tree = Node::new(200);
+        assert_eq!(tree.values, [200]);
+        assert_eq!(tree.nodes.len(), 0);
+    }
+
+    #[test]
+    fn test_iter() {
+        let mut tree = Node::new(200);
+        tree.iter();
+        assert_eq!(tree.nodes.len(), 1);
+        assert_eq!(tree.nodes[0].values, vec![100, 100]);
+    }
+
+    #[test]
+    fn test_iter_2() {
+        let mut tree = Node::new(200);
+        tree.iter();
+        tree.iter();
+        assert_eq!(tree.nodes[0][0].values, vec![50, 50, 100]);
+        assert_eq!(tree.nodes[0][1].values, vec![50; 4]);
+    }
+}