Merge pull request youngyangyang04#813 from casnz1601/patch-2

Update 0257.二叉树的所有路径.md

problems/0257.二叉树的所有路径.md

@@ -404,33 +404,41 @@ class Solution {
     }
 }
 ```
-
-Python：
-```Python
+---
+Python:  
+递归法+隐形回溯
+```Python3
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
 class Solution:
-    """二叉树的所有路径 递归法"""
-
     def binaryTreePaths(self, root: TreeNode) -> List[str]:
-        path, result = '', []
+        path = ''
+        result = []
+        if not root: return result
         self.traversal(root, path, result)
         return result
 
-    def traversal(self, cur: TreeNode, path: List, result: List):
+    def traversal(self, cur: TreeNode, path: str, result: List[str]) -> None:
         path += str(cur.val)
-        # 如果当前节点为叶子节点，添加路径到结果中
-        if not (cur.left or cur.right):
+        # 若当前节点为leave，直接输出
+        if not cur.left and not cur.right:
             result.append(path)
-            return
-
+
         if cur.left:
+            # + '->' 是隐藏回溯
             self.traversal(cur.left, path + '->', result)
-            
+
         if cur.right:
             self.traversal(cur.right, path + '->', result)
-
 ```
-
-```python
+
+迭代法：
+
+```python3
 from collections import deque
 
 
@@ -457,7 +465,8 @@ class Solution:
 
         return result
 ```
-
+
+---
 
 Go：
 ```go
@@ -482,7 +491,7 @@ func binaryTreePaths(root *TreeNode) []string {
     return res
 }
 ```
-
+---
 JavaScript:
 
 1.递归版本