Swift: 计算二叉树的最大深度

/**

• Definition for a binary tree node.
• public class TreeNode {

• public var val: Int
  

• public var left: TreeNode?
  

• public var right: TreeNode?
  

• public init() { self.val = 0; self.left = nil; self.right = nil; }
  

• public init(_ val: Int) { self.val = val; self.left = nil; self.right = nil; }
  

• public init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
  

•     self.val = val
  

•     self.left = left
  

•     self.right = right
  

• }
  

• } */ class Solution { func maxDepth(_ root: TreeNode?) -> Int { if root == nil { return 0 } return max(maxDepth(root.left), maxDepth(root.right)) + 1 } }//如果仍然报（TreeNode已定义且要导入的库都已导入）错误，请检查您的代码是否正确导入和引用了TreeNode类。