feat: add swift implementation to lcp problem: No.67 (#4026)

lcp/LCP 67. 装饰树/README.md

@@ -197,6 +197,46 @@ func expandBinaryTree(root *TreeNode) *TreeNode {
 }
 ```
 
+#### Swift
+
+```swift
+/* class TreeNode {
+*     var val: Int
+*     var left: TreeNode?
+*     var right: TreeNode?
+*     init() { self.val = 0; self.left = nil; self.right = nil }
+*     init(_ val: Int) { self.val = val; self.left = nil; self.right = nil }
+*     init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+*         self.val = val
+*         self.left = left
+*         self.right = right
+*     }
+* }
+*/
+
+class Solution {
+    func expandBinaryTree(_ root: TreeNode?) -> TreeNode? {
+        return dfs(root)
+    }
+
+    private func dfs(_ root: TreeNode?) -> TreeNode? {
+        guard let root = root else { return nil }
+
+        let leftChild = dfs(root.left)
+        let rightChild = dfs(root.right)
+
+        if let leftChild = leftChild {
+            root.left = TreeNode(-1, leftChild, nil)
+        }
+        if let rightChild = rightChild {
+            root.right = TreeNode(-1, nil, rightChild)
+        }
+        return root
+    }
+}
+
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcp/LCP 67. 装饰树/Solution.swift

@@ -0,0 +1,36 @@
+/* class TreeNode {
+*     var val: Int
+*     var left: TreeNode?
+*     var right: TreeNode?
+    
+*     init() { self.val = 0; self.left = nil; self.right = nil }
+*     init(_ val: Int) { self.val = val; self.left = nil; self.right = nil }
+*     init(_ val: Int, _ left: TreeNode?, _ right: TreeNode?) {
+*         self.val = val
+*         self.left = left
+*         self.right = right
+*     }
+* }
+*/
+
+class Solution {
+    func expandBinaryTree(_ root: TreeNode?) -> TreeNode? {
+        return dfs(root)
+    }
+    
+    private func dfs(_ root: TreeNode?) -> TreeNode? {
+        guard let root = root else { return nil }
+        
+        let leftChild = dfs(root.left)
+        let rightChild = dfs(root.right)
+        
+        if let leftChild = leftChild {
+            root.left = TreeNode(-1, leftChild, nil)
+        }
+        if let rightChild = rightChild {
+            root.right = TreeNode(-1, nil, rightChild)
+        }
+        
+        return root
+    }
+}