https://leetcode.com/problems/symmetric-tree/

    1. /**
    2.  * Definition for a binary tree node.
    3.  * type TreeNode struct {
    4.  *     Val int
    5.  *     Left *TreeNode
    6.  *     Right *TreeNode
    7.  * }
    8.  */
    9. func isSymmetric(root *TreeNode) bool {
    10.     if root == nil {
    11.         return true
    12.     }
    14.     return isSymmetricTrack(root.Left, root.Right)
    15. }
    17. func isSymmetricTrack(p *TreeNode, q *TreeNode) bool{
    18.     if p == nil && q == nil {
    19.         return true
    20.     }
    22.     if p == nil || q == nil {
    23.         return false
    24.     }
    26.     return (p.Val == q.Val) && isSymmetricTrack(p.Left, q.Right) && isSymmetricTrack(p.Right, q.Left)
    27. }