diff --git a/src/leetcode/diameter_of_binary_tree_543/mod.rs b/src/leetcode/diameter_of_binary_tree_543/mod.rs
new file mode 100644
index 0000000..8938348
--- /dev/null
+++ b/src/leetcode/diameter_of_binary_tree_543/mod.rs
@@ -0,0 +1,109 @@
+use std::{cell::RefCell, collections::VecDeque, ops::Deref, rc::Rc};
+pub struct Solution;
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct TreeNode {
+    pub val: i32,
+    pub left: Option<Rc<RefCell<TreeNode>>>,
+    pub right: Option<Rc<RefCell<TreeNode>>>,
+}
+
+impl TreeNode {
+    #[inline]
+    pub fn new(val: i32) -> Self {
+        TreeNode {
+            val,
+            left: None,
+            right: None,
+        }
+    }
+}
+
+impl Solution {
+    pub fn diameter_of_binary_tree(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
+        match root {
+            None => 0,
+            Some(root) => {
+                Self::get_height(
+                    root.deref()
+                        .borrow()
+                        .right
+                        .as_ref()
+                        .map(|right| right.clone()),
+                ) + Self::get_height(root.deref().borrow().left.as_ref().map(|left| left.clone()))
+            }
+        }
+    }
+    fn get_height(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
+        match root {
+            None => 0,
+            Some(root) => {
+                let mut count = 0;
+                let mut stack = VecDeque::new();
+                stack.push_back(root);
+                while !stack.is_empty() {
+                    count += 1;
+                    let visiting = stack.pop_back().unwrap();
+                    if let Some(right) = visiting.deref().borrow().right.clone() {
+                        stack.push_back(right);
+                    }
+                    if let Some(left) = visiting.deref().borrow().left.clone() {
+                        stack.push_back(left);
+                    };
+                }
+                return ((count + 1) as f32).log2().floor() as i32;
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use test_case::test_case;
+
+    fn build_binary_tree(elements: &[i32]) -> Option<Rc<RefCell<TreeNode>>> {
+        let mut tree = None;
+        if elements.is_empty() {
+            return tree;
+        }
+        'insert: for n in elements.iter() {
+            if tree.is_none() {
+                tree = Some(Rc::new(RefCell::new(TreeNode::new(*n))));
+                continue;
+            }
+            let mut queue = vec![tree.as_ref().unwrap().clone()];
+            while !queue.is_empty() {
+                let current = queue.pop().unwrap();
+                match &mut current.deref().borrow_mut().left {
+                    Some(left) => {
+                        queue.push(left.clone());
+                    }
+                    left @ None => {
+                        *left = Some(Rc::new(RefCell::new(TreeNode::new(*n))));
+                        continue 'insert;
+                    }
+                }
+                match &mut current.deref().borrow_mut().right {
+                    Some(right) => {
+                        queue.push(right.clone());
+                    }
+                    right @ None => {
+                        *right = Some(Rc::new(RefCell::new(TreeNode::new(*n))));
+                        continue 'insert;
+                    }
+                };
+            }
+        }
+        tree
+    }
+
+    #[test_case(&[1,2,3,4,5] => 3; "example 1")]
+    #[test_case(&[1,2] => 1; "case 1")]
+    #[test_case(&[1] => 0; "case 2")]
+    // -1 is a sentinel value, meaning null
+    #[test_case(&[2,3,-1,1] => 2; "case 3")]
+    fn test_solution(elements: &[i32]) -> i32 {
+        Solution::diameter_of_binary_tree(build_binary_tree(elements))
+    }
+}
diff --git a/src/leetcode/mod.rs b/src/leetcode/mod.rs
index cbbbe1e..f9913fc 100644
--- a/src/leetcode/mod.rs
+++ b/src/leetcode/mod.rs
@@ -1,3 +1,4 @@
+pub mod diameter_of_binary_tree_543;
 pub mod bitwise_and_of_numbers_range_201;
 pub mod implement_trie_208;
 pub mod add_two_numbers_2;