update 二叉树理论基础.md about rust

problems/二叉树理论基础.md

@@ -270,6 +270,29 @@ class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null)
   var right: TreeNode = _right
 }
 ```
+
+rust:
+
+```rust
+#[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,
+        }
+    }
+}
+```
+
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