From b80c96299f9ab401df4318d989c8b16722243a9d Mon Sep 17 00:00:00 2001
From: Lanre Adedara <lanre.adedara@shara.co>
Date: Tue, 4 Jun 2024 07:53:33 +0100
Subject: [PATCH] feat: add swift implementation to lcof2 problem: No.028

---
 .../README.md"                                | 48 +++++++++++++++++++
 .../Solution.swift"                           | 43 +++++++++++++++++
 2 files changed, 91 insertions(+)
 create mode 100644 "lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/Solution.swift"

diff --git "a/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/README.md" "b/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/README.md"
index 19759fc442666..2be6abf311439 100644
--- "a/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/README.md"	
+++ "b/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/README.md"	
@@ -244,6 +244,54 @@ public:
 };
 ```
 
+#### Swift
+
+```swift
+/* class Node {
+*     var val: Int
+*     var prev: Node?
+*     var next: Node?
+*     var child: Node?
+
+*     init(_ val: Int) {
+*         self.val = val
+*         self.prev = nil
+*         self.next = nil
+*         self.child = nil
+*     }
+* }
+*/
+
+class Solution {
+    private var dummy = Node(0)
+    private var tail: Node?
+
+    func flatten(_ head: Node?) -> Node? {
+        guard let head = head else {
+            return nil
+        }
+        tail = dummy
+        preOrder(head)
+        dummy.next?.prev = nil
+        return dummy.next
+    }
+
+    private func preOrder(_ node: Node?) {
+        guard let node = node else {
+            return
+        }
+        let next = node.next
+        let child = node.child
+        tail?.next = node
+        node.prev = tail
+        tail = node
+        node.child = nil
+        preOrder(child)
+        preOrder(next)
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->
diff --git "a/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/Solution.swift" "b/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/Solution.swift"
new file mode 100644
index 0000000000000..710a1f3a4e2f1
--- /dev/null
+++ "b/lcof2/\345\211\221\346\214\207 Offer II 028. \345\261\225\345\271\263\345\244\232\347\272\247\345\217\214\345\220\221\351\223\276\350\241\250/Solution.swift"	
@@ -0,0 +1,43 @@
+/* class Node {
+*     var val: Int
+*     var prev: Node?
+*     var next: Node?
+*     var child: Node?
+
+*     init(_ val: Int) {
+*         self.val = val
+*         self.prev = nil
+*         self.next = nil
+*         self.child = nil
+*     }
+* }
+*/
+
+class Solution {
+    private var dummy = Node(0)
+    private var tail: Node?
+
+    func flatten(_ head: Node?) -> Node? {
+        guard let head = head else {
+            return nil
+        }
+        tail = dummy
+        preOrder(head)
+        dummy.next?.prev = nil
+        return dummy.next
+    }
+
+    private func preOrder(_ node: Node?) {
+        guard let node = node else {
+            return
+        }
+        let next = node.next
+        let child = node.child
+        tail?.next = node
+        node.prev = tail
+        tail = node
+        node.child = nil
+        preOrder(child)
+        preOrder(next)
+    }
+}
\ No newline at end of file