diff --git a/src/data_struct/linked_hashmap.rs b/src/data_struct/linked_hashmap.rs
new file mode 100644
index 00000000..bf4d8949
--- /dev/null
+++ b/src/data_struct/linked_hashmap.rs
@@ -0,0 +1,224 @@
+use std::{
+    collections::{hash_map::Entry, HashMap},
+    hash::Hash,
+};
+
+use crate::Error;
+
+struct LinkedEntry<K, V>
+where
+    V: Clone,
+{
+    value: V,
+    next_key: Option<K>,
+}
+
+impl<K, V> LinkedEntry<K, V>
+where
+    V: Clone,
+{
+    pub fn new(value: V) -> Self {
+        LinkedEntry {
+            value,
+            next_key: None,
+        }
+    }
+
+    pub fn get_value(&self) -> &V {
+        &self.value
+    }
+}
+
+struct LinkedHashMapIterator<'a, K, V>
+where
+    V: Clone,
+    K: Hash + Eq + PartialEq + Clone + PartialOrd + Ord,
+{
+    lhm: &'a LinkedHashMap<K, V>,
+    current_key: Option<&'a K>,
+}
+
+impl<'a, K, V> Iterator for LinkedHashMapIterator<'a, K, V>
+where
+    V: Clone,
+    K: Hash + Eq + PartialEq + Clone + PartialOrd + Ord,
+{
+    type Item = &'a V;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(key) = self.current_key {
+            match self.lhm.get_link_entry(key) {
+                Some(entry) => {
+                    self.current_key = entry.next_key.as_ref();
+                    Some(entry.get_value())
+                }
+                None => None,
+            }
+        } else {
+            None
+        }
+    }
+}
+
+#[derive(Default)]
+pub struct LinkedHashMap<K, V>
+where
+    K: Hash + PartialEq + Eq + Clone + PartialOrd + Ord,
+    V: Clone,
+{
+    map: HashMap<K, LinkedEntry<K, V>>,
+    roots: Vec<K>,
+}
+
+impl<K, V> LinkedHashMap<K, V>
+where
+    K: Hash + PartialEq + Eq + Clone + PartialOrd + Ord,
+    V: Clone,
+{
+    pub fn new() -> Self {
+        Self {
+            map: HashMap::new(),
+            roots: Vec::new(),
+        }
+    }
+
+    pub fn with_capacity(capacity: usize) -> Self {
+        Self {
+            map: HashMap::with_capacity(capacity),
+            roots: Vec::with_capacity(capacity),
+        }
+    }
+
+    pub fn insert_root(&mut self, key: K, value: V) -> Result<(), Error> {
+        match self.map.entry(key.clone()) {
+            Entry::Occupied(_) => Err(Error::KeyError("Key is already used".to_string())),
+            Entry::Vacant(entry) => {
+                entry.insert(LinkedEntry::new(value));
+                self.roots.push(key);
+                self.roots.sort(); // allow binary search when removing root
+                Ok(())
+            }
+        }
+    }
+
+    pub fn insert(&mut self, parent_key: &K, key: K, value: V) -> Result<(), Error> {
+        let parent_entry = match self.map.get(parent_key) {
+            Some(linked_entry) => Ok(linked_entry),
+            None => Err(Error::KeyError("Parent key not found".to_string())),
+        }?;
+
+        if parent_entry.next_key.is_some() {
+            return Err(Error::KeyError(
+                "Parent already contains a next key".to_string(),
+            ));
+        }
+
+        match self.map.entry(key.clone()) {
+            Entry::Occupied(_) => Err(Error::KeyError("Key is already used".to_string())),
+            Entry::Vacant(entry) => {
+                entry.insert(LinkedEntry::new(value));
+                // cannot hold mutable reference from parent_entry
+                self.map
+                    .get_mut(parent_key)
+                    .expect("checked above")
+                    .next_key = Some(key);
+                Ok(())
+            }
+        }
+    }
+
+    pub fn get(&self, key: &K) -> Option<&V> {
+        self.map.get(key).map(LinkedEntry::get_value)
+    }
+
+    fn get_link_entry(&self, key: &K) -> Option<&LinkedEntry<K, V>> {
+        self.map.get(key)
+    }
+
+    pub fn iter_link<'a>(&'a self, key: &'a K) -> impl Iterator<Item = &V> + 'a {
+        LinkedHashMapIterator::<'a, K, V> {
+            lhm: self,
+            current_key: Some(key),
+        }
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = (&K, &V)> {
+        self.map.iter().map(|(k, entry)| (k, &entry.value))
+    }
+
+    /// Remove all but the last (key, value) pair from a link
+    pub fn pop_link(&mut self, root_key: K) -> Result<(), Error> {
+        let root_index = self
+            .roots
+            .binary_search(&root_key)
+            .map_err(|_| Error::KeyError("Root key not found".to_string()))?;
+
+        /*match self.map.entry(root_key) {
+            Entry::Occupied(e) => match &e.get().next_key {
+                Some(next_key) => todo!(),
+                None => (),
+            },
+            Entry::Vacant(_) => (),
+        }*/
+
+        if let Entry::Occupied(root_entry) = self.map.entry(root_key) {
+            let mut curr_entry = root_entry;
+
+            while let Some(next_key) = curr_entry.get_mut().next_key.take() {
+                //self.roots[root_index] =
+                curr_entry.remove_entry();
+                curr_entry = match self.map.entry(next_key) {
+                    Entry::Occupied(e) => e,
+                    Entry::Vacant(_) => {
+                        return Err(Error::KeyError("Key not found".to_string()));
+                    }
+                }
+            }
+        } else {
+            return Err(Error::KeyError("Root key not found".to_string()));
+        }
+
+        todo!()
+
+        /*if let Some(root_entry) = self.map.entry(root_key) {
+            /*let mut curr_entry = root_entry;
+            while let Some(next_key) = curr_entry.next_key.as_ref() {
+                match self.get_link_entry(next_key) {
+                    Some(entry) => {
+                        curr_entry = entry;
+                    }
+                    None => return Err(Error::KeyError("Key not found".to_string())),
+                }
+            }
+            // curr_entry is the last entry in the chain
+            self.roots[root_index] = root_key.clone();*/
+            Ok(())
+        } else {
+            Err(Error::KeyError("Root key not found".to_string()))
+        }*/
+    }
+}
+
+#[test]
+fn test_linked_hashmap() -> Result<(), Error> {
+    let mut lhm = LinkedHashMap::new();
+
+    lhm.insert_root(1, "key1".to_string())?;
+    lhm.insert_root(2, "key2".to_string())?;
+    lhm.insert_root(3, "key3".to_string())?;
+
+    lhm.insert(&1, 11, "key11".to_string())?;
+    assert!(lhm.insert(&1, 12, "key12".to_string()).is_err());
+    lhm.insert(&11, 111, "key111".to_string())?;
+
+    assert_eq!(lhm.get(&1), Some(&"key1".to_string()));
+    assert_eq!(lhm.get(&11), Some(&"key11".to_string()));
+
+    let res: Vec<_> = lhm.iter().collect();
+    assert_eq!(res.len(), lhm.map.len());
+
+    let res: Vec<_> = lhm.iter_link(&1).collect();
+    assert_eq!(res, vec!["key1", "key11", "key111"]);
+
+    Ok(())
+}
diff --git a/src/data_struct/mod.rs b/src/data_struct/mod.rs
new file mode 100644
index 00000000..54bd8bbb
--- /dev/null
+++ b/src/data_struct/mod.rs
@@ -0,0 +1,3 @@
+pub mod linked_hashmap;
+
+use linked_hashmap::LinkedHashMap;