rs: add “104. Maximum Depth of Binary Tree”

Signed-off-by: Matej Focko <mfocko@redhat.com>

rs/maximum-depth-of-binary-tree.rs

@@ -0,0 +1,38 @@
+// Definition for a binary tree node.
+// #[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
+//     }
+//   }
+// }
+
+use std::rc::Rc;
+use std::cmp;
+use std::cell::RefCell;
+
+fn _max_depth(root: Option<Rc<RefCell<TreeNode>>>, depth: i32) -> i32 {
+    match root {
+        None => depth,
+        Some(node) => cmp::max(
+            _max_depth(node.borrow().left.clone(), depth + 1),
+            _max_depth(node.borrow().right.clone(), depth + 1),
+        ),
+    }
+}
+
+impl Solution {
+    pub fn max_depth(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
+        _max_depth(root, 0)
+    }
+}