101. Symmetric Tree (Easy) - TengnanYao/daily_leetcode GitHub Wiki

# 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
        """
        if not root:
            return True
        def dfs(L, R):
            if L and R:
                return L.val == R.val and dfs(L.left, R.right) and dfs(R.left, L.right)
            return L is R
        return dfs(root.left, root.right)