Update 0112.路径总和.md

python version of code added

problems/0112.路径总和.md

@@ -348,8 +348,32 @@ class Solution {
 ```
 
 Python：
+```python
+// 递归法
+# 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:
+    def hasPathSum(self, root: TreeNode, targetSum: int) -> bool:
+        def isornot(root,targetSum)->bool:
+            if (not root.left) and (not root.right) and targetSum == 0:return True // 遇到叶子节点，并且计数为0
+            if (not root.left) and (not root.right):return False //遇到叶子节点，计数不为0
+            if root.left:
+                targetSum -= root.left.val  //只有左节点
+                if isornot(root.left,targetSum):return True  //递归，处理节点
+                targetSum += root.left.val  //回溯
+            if root.right:
+                targetSum -= root.right.val //只有右节点
+                if isornot(root.right,targetSum):return True //递归，处理右节点
+                targetSum += root.right.val //回溯
+            return False
             
-
+        if root == None:return False  //别忘记处理空TreeNode
+        else:return isornot(root,targetSum-root.val)
+```
 Go：
 
 JavaScript：