题目描述

代码实现

class Solution {
    func maxDepth(_ root: TreeNode?) -> Int {
        guard root != nil else {
            return 0
        }
        let leftDepth = maxDepth(root!.left)
        let rightDepth = maxDepth(root!.right)
        return max(leftDepth, rightDepth) + 1
    }
}

Q.E.D.