0101-symmetric-tree¶

Description¶

Given the root of a binary tree, check whether it is a mirror of itself (i.e., symmetric around its center).

Example 1:

Input: root = [1,2,2,3,4,4,3]
Output: true

Example 2:

Input: root = [1,2,2,null,3,null,3]
Output: false

Constraints:

The number of nodes in the tree is in the range [1, 1000].
-100 <= Node.val <= 100

Follow up: Could you solve it both recursively and iteratively?

Solution(Python)¶

# 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: TreeNode | None) -> bool:
        if not root:
            return True
        return self.isMirror(root.left, root.right)
        
    def isMirror(self, t1: TreeNode, t2: TreeNode) -> bool:
        if not t1 and not t2:
            return True
        if not t1 or not t2:
            return False
        return (t1.val == t2.val and 
                self.isMirror(t1.left, t2.right) and 
                self.isMirror(t1.right, t2.left))
        