O(n) time and O(n) space using Deque(Iterative)

Author: 149ps

101. Symmetric Tree/101. Symmetric Tree_1.py

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+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def isSymmetric(self, root: TreeNode) -> bool:
+        if not root:
+            return True
+        q = collections.deque()
+        q.append(root)
+        q.append(root)
+        while q:
+            node1 = q.popleft()
+            node2 = q.popleft()
+            if not node1 and not node2:
+                continue
+            if not node1 or not node2:
+                return False
+            if node1.val != node2.val:
+                return False
+            q.append(node1.left)
+            q.append(node2.right)
+            q.append(node1.right)
+            q.append(node2.left)
+        return True