Swift 二叉树的最大深度- LeetCode

    3
   / \
  9  20
    /  \
   15   7

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     public var val: Int
 *     public var left: TreeNode?
 *     public var right: TreeNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.left = nil
 *         self.right = nil
 *     }
 * }
 */
class Solution {
    func maxDepth(_ root: TreeNode?) -> Int {
        if root == nil {
            return 0
        }
        return (1 + max(maxDepth(root?.left), maxDepth(root?.right)))
    }
}