O(n) time and O(logn) space for recursive stack

Author: 149ps

116. Populating Next Right Pointers in Each Node/116. Populating Next Right Pointers in Each Node.py

@@ -28,16 +28,13 @@ def __init__(self, val, left, right, next):
         self.next = next
 """
 class Solution:
-    def connect(self, root: 'Node') -> 'Node':
-        if not root:
-            return None
-        if root.left:
-            root.left.next = root.right
+    def connect(self, root: 'Optional[Node]') -> 'Optional[Node]':
+        if not root: return None
         if root.right:
+            if root.left:
+                root.left.next = root.right
             if root.next:
                 root.right.next = root.next.left
-            else:
-                root.right.next = None
         self.connect(root.left)
         self.connect(root.right)
         return root