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[101] Symmetric Tree

https://leetcode.com/problems/symmetric-tree/description/

algorithms
Easy (41.85%)
Source Code: 101.symmetric-tree.py
Total Accepted: 383.6K
Total Submissions: 889.2K
Testcase Example: '[1,2,2,3,4,4,3]'

Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).

For example, this binary tree [1,2,2,3,4,4,3] is symmetric:

/
2 2 / \ /
3 4 4 3

But the following [1,2,2,null,3,null,3] is not:

/
2 2 \
3 3

Note: Bonus points if you could solve it both recursively and iteratively.

python

# 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 not root or not root.left and not root.right: return True

        new_tree = self.buildTree(root)

        return self.sameTree(root, new_tree)

    def buildTree(self, root):
        if not root: return None
        new_tree = TreeNode(root.val)
        new_tree.left = self.buildTree(root.right)
        new_tree.right = self.buildTree(root.left)
        return new_tree

    def sameTree(self, root, new_tree):
        if not root and not new_tree: return True
        if not root and new_tree or root and not new_tree: return False

        if not root.val == new_tree.val: return False

        return self.sameTree(root.left, new_tree.left) and self.sameTree(root.right, new_tree.right)