(Iteratively)_Symmetric_Tree

CodingProgrammer · CodingProgrammer · commit 75175f04854c · 2017-12-22T09:33:32.000+08:00
diff --git a/101(Iteratively)_Symmetric_Tree.py b/101(Iteratively)_Symmetric_Tree.py
@@ -0,0 +1,31 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    
+    def isSymmetric(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        if root is None:
+            return True
+        stack = [[root.left, root.right]]
+        while len(stack) > 0:
+            pair = stack.pop(0)
+            left = pair[0]
+            right = pair[1]
+            if None == left and None == right:
+                continue
+            elif None == left or None == right:
+                return False
+            elif left.val == right.val:
+                stack.insert(0,[left.left, right.right])
+                stack.insert(0,[left.right, right.left])
+            else:
+                return False
+        return True
