第十周作业2

// A code block
func isSymmetric(root *TreeNode) bool { 
   return dfs(root, root)}
func dfs(p *TreeNode, q *TreeNode) bool { 
   if p == nil || q == nil {     
      return p == q    }   
       return dfs(p.Left, q.Right) && p.Val == q.Val && dfs(p.Right, q.Left)}