Update 0797.所有可能的路径.md

添加Python实现

problems/0797.所有可能的路径.md

@@ -296,5 +296,29 @@ public:
 ### Java 
 
 ### Python
+```
+class Solution:
+    def __init__(self):
+        self.result = []
+        self.path = [0]
+
+    def allPathsSourceTarget(self, graph: List[List[int]]) -> List[List[int]]:
+        if not graph: return []
+
+        self.dfs(graph, 0)
+        return self.result
+    
+    def dfs(self, graph, root: int):
+        if root == len(graph) - 1:  # 成功找到一条路径时
+            # ***Python的list是mutable类型***
+            # ***回溯中必须使用Deep Copy***
+            self.result.append(self.path[:]) 
+            return
+        
+        for node in graph[root]:   # 遍历节点n的所有后序节点
+            self.path.append(node)
+            self.dfs(graph, node)
+            self.path.pop() # 回溯
+```
 
 ### Go