Leetcode symmetric tree

tree.md

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+# Binary tree
+
++ [Symmetric Tree (euler path)](#symmetric-tree-euler-path)
++ [Symmetric Tree (recursive)](#symmetric-tree-recursive)
+
+## Symmetric Tree (euler path)
+
+https://leetcode.com/problems/symmetric-tree/
+
+```python
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution(object):
+    def isSymmetric(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        path = []
+
+        def euler(node):
+            if not node:
+                path.append(None)
+                return
+
+            path.append(node.val)
+            euler(node.left)
+            path.append(node.val)
+            euler(node.right)
+            path.append(node.val)
+
+        euler(root)
+        return path == path[::-1]
+
+```
+
+## Symmetric Tree (recursive)
+
+https://leetcode.com/problems/symmetric-tree/
+
+```python
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def isSymmetric(self, root):
+        """
+        :type root: TreeNode
+        :rtype: bool
+        """
+        if not root:
+            return True
+
+        def isSymmetricBst(nodeA, nodeB):
+            """
+            :type nodeA: TreeNode
+            :type nodeB: TreeNode
+            :rtype: bool
+            """
+            if not nodeA and not nodeB:
+                return True
+            elif not (nodeA and nodeB):
+                return False
+            else:
+                return nodeA.val == nodeB.val and isSymmetricBst(nodeA.left, nodeB.right) and isSymmetricBst(
+                    nodeA.right,
+                    nodeB.left)
+
+        return isSymmetricBst(root.left, root.right)
+
+```