101. Symmetric Tree.md

Leetcode 101. Symmetric Tree

Runtime: 54 ms, faster than 39.25% of Python3

# Time Complexity 
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right

class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        
        res = []
        level = 0
        
        def traverse(root, level):
            
            if not root:
                try:
                    res[level]
                except Exception:
                    res.append([])
                res[level].append(None)
                return 0
            
            try:
                res[level]
            except Exception:
                res.append([])
            res[level].append(root.val)
            
            level += 1
            traverse(root.left, level)
            traverse(root.right, level)
            
        traverse(root, level)
        
        for i in res:
            if i != i[::-1]:
                return False
            
        return True