AC. Use Queue. 384ms.

297. Serialize and Deserialize Binary Tree.py

@@ -7,14 +7,16 @@
 
 from queue import Queue
 
-class Codec:
 
+class Codec:
     def serialize(self, root):
         """Encodes a tree to a single string.
         
         :type root: TreeNode
         :rtype: str
         """
+        if not root:
+            return ''
         lst = []
         q = Queue()
         q.put(root)
@@ -27,27 +29,52 @@ def serialize(self, root):
             q.put(node.left)
             q.put(node.right)
         return ','.join(str(x) for x in lst)
-
 
     def deserialize(self, data):
         """Decodes your encoded data to tree.
         
         :type data: str
         :rtype: TreeNode
         """
-        def construct(lst, idx):
-            if lst[idx] is None:
-                return None
-            node = TreeNode(lst[idx])
-            left = idx * 2 + 1
-            right = idx * 2 + 2
-            if left < len(lst):
-                node.left = construct(lst, left)
-                node.right = construct(lst, right)
-            return node
-
-        lst = [int(x) if x.lstrip('-').isdigit() else None for x in data.split(',')]
-        return construct(lst,0)
+        if not data:
+            return None
+        lst = [
+            int(x) if x.lstrip('-').isdigit() else None
+            for x in data.split(',')
+        ]
+        q = Queue()
+        root = TreeNode(lst[0])
+        q.put(root)
+        length = len(lst)
+        idx = 0
+        while not q.empty():
+            node = q.get()
+            idx += 1
+            if idx == length:
+                break
+            if lst[idx] is not None:
+                left = TreeNode(lst[idx])
+                node.left = left
+                q.put(left)
+            idx += 1
+            if idx == length: break
+            if lst[idx] is not None:
+                right = TreeNode(lst[idx])
+                node.right = right
+                q.put(right)
+
+        return root
+
+        # def construct(lst, idx):
+        #     if lst[idx] is None:
+        #         return None
+        #     node = TreeNode(lst[idx])
+        #     left = idx * 2 + 1
+        #     right = idx * 2 + 2
+        #     if left < len(lst):
+        #         node.left = construct(lst, left)
+        #         node.right = construct(lst, right)
+        #     return node
 
 
 # Your Codec object will be instantiated and called as such: