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// @Title: 对称的二叉树 (对称的二叉树  LCOF)
// @Author: 15816537946@163.com
// @Date: 2022-02-12 16:42:24
// @Runtime: 0 ms
// @Memory: 2.7 MB
/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */
func isSymmetric(root *TreeNode) bool {
    if root == nil {
        return true
    }

    return helper(root.Left, root.Right)
}

func helper(left, right *TreeNode) bool {
    if left == nil && right == nil {
        return true
    }
    if left == nil || right ==nil || left.Val != right.Val {
        return false
    }
    return helper(left.Left,right.Right) && helper(left.Right, right.Left)
}