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Leetcode 101 对称二叉树

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给你一个二叉树的根节点 root ， 检查它是否 轴对称 。

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# 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

# 递归
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        def helper(left_tree, right_tree):
            if not left_tree and not right_tree: return True
            if left_tree and right_tree:
                if left_tree.val == right_tree.val and helper(left_tree.right, right_tree.left) and helper(left_tree.left, right_tree.right):
                    return True
            return False
        return helper(root.left, root.right)
    
# 迭代
class Solution:
    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
        queue = [root, root]
        while queue:
            cur_left, cur_right = queue[0], queue[1]
            if not cur_left and not cur_right: 
                queue = queue[2:]
                continue
            if not cur_left or not cur_right or cur_left.val != cur_right.val:
                return False
            queue.append(cur_left.left)
            queue.append(cur_right.right)
            queue.append(cur_left.right)
            queue.append(cur_right.left)
            queue = queue[2:]
        return True