feat: add swift implementation to lcof problem: No.55.1 (#2941)

Author: klever34

lcof/面试题55 - I. 二叉树的深度/README.md

@@ -218,6 +218,31 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+/* 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 {
+        guard let root = root else {
+            return 0
+        }
+        return 1 + max(maxDepth(root.left), maxDepth(root.right))
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题55 - I. 二叉树的深度/Solution.swift

@@ -0,0 +1,20 @@
+/* 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 {
+        guard let root = root else {
+            return 0
+        }
+        return 1 + max(maxDepth(root.left), maxDepth(root.right))
+    }
+}