Update 0112.路径总和.md

增加：0113 - python - 迭代法 - 前序遍历解法

problems/0112.路径总和.md

@@ -560,6 +560,26 @@ class Solution:
         return result
 ```
 
+**迭代法，前序遍历**
+
+```python
+class Solution:
+    def pathSum(self, root: Optional[TreeNode], targetSum: int) -> List[List[int]]:
+        if not root: return []
+        stack, path_stack,result = [[root,root.val]],[[root.val]],[]
+        while stack:
+            cur,cursum = stack.pop()
+            path = path_stack.pop()
+            if cur.left==cur.right==None:
+                if cursum==targetSum: result.append(path)
+            if cur.right:
+                stack.append([cur.right,cursum+cur.right.val])
+                path_stack.append(path+[cur.right.val])
+            if cur.left: 
+                stack.append([cur.left,cursum+cur.left.val])
+                path_stack.append(path+[cur.left.val])
+        return result
+```
 ## go
 
 ### 112. 路径总和