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Author: Chris Wu

problems/symmetric-tree.py

@@ -15,4 +15,22 @@ def isSymmetric(self, root):
                 if left_node.val!=right_node.val: return False
                 q.append((left_node.right, right_node.left))
                 q.append((left_node.left, right_node.right))
-        return True
+        return True
+
+
+# class Solution(object):
+#     def isSymmetric(self, root):
+#         if not root: return True
+        
+#         stack = []
+#         stack.append((root.left, root.right))
+#         while stack:
+#             left_node, right_node = stack.pop()
+#             if not left_node and right_node: return False
+#             if not right_node and left_node: return False
+            
+#             if left_node and right_node:
+#                 if left_node.val!=right_node.val: return False
+#                 stack.append((left_node.right, right_node.left))
+#                 stack.append((left_node.left, right_node.right))
+#         return True