# ---
# title: 101. Symmetric Tree
# id: problem101
# author: Tian Jun
# date: 2020-10-31
# difficulty: Easy
# categories: Tree, Depth-first Search, Breadth-first Search
# link: <https://leetcode.com/problems/symmetric-tree/description/>
# hidden: true
# ---
# 
# 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:
# 
#     
#     
#         1
#        / \
#       2   2
#      / \ / \
#     3  4 4  3
#     
# 
# 
# 
# But the following `[1,2,2,null,3,null,3]` is not:
# 
#     
#     
#         1
#        / \
#       2   2
#        \   \
#        3    3
#     
# 
# 
# 
# **Follow up:** Solve it both recursively and iteratively.
# 
# 
## @lc code=start
using LeetCode

## add your code here:
## @lc code=end
