Update 二叉树中递归带着回溯.md

problems/二叉树中递归带着回溯.md

@@ -649,6 +649,43 @@ impl Solution {
 }
 ```
 
+> 257.二叉树的不同路径
+
+```rust
+// 递归
+use std::cell::RefCell;
+use std::rc::Rc;
+impl Solution {
+    pub fn binary_tree_paths(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<String> {
+        let mut res = vec![];
+        let mut path = vec![];
+        Self::recur(&root, &mut path, &mut res);
+        res
+    }
+
+    pub fn recur(
+        root: &Option<Rc<RefCell<TreeNode>>>,
+        path: &mut Vec<String>,
+        res: &mut Vec<String>,
+    ) {
+        let node = root.as_ref().unwrap().borrow();
+        path.push(node.val.to_string());
+        if node.left.is_none() && node.right.is_none() {
+            res.push(path.join("->"));
+            return;
+        }
+        if node.left.is_some() {
+            Self::recur(&node.left, path, res);
+            path.pop(); //回溯
+        }
+        if node.right.is_some() {
+            Self::recur(&node.right, path, res);
+            path.pop(); //回溯
+        }
+    }
+}
+```
+
 
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