feat: add swift implementation to lcof problem: No.25 (doocs#2892)

Author: klever34

lcof/面试题25. 合并两个排序的链表/README.md

@@ -311,6 +311,44 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+/* public class ListNode {
+*     var val: Int
+*     var next: ListNode?
+*     init(_ val: Int) {
+*         self.val = val
+*         self.next = nil
+*     }
+* }
+*/
+
+class Solution {
+    func mergeTwoLists(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
+        let dummy = ListNode(0)
+        var cur: ListNode? = dummy
+        var l1 = l1
+        var l2 = l2
+        
+        while let l1Node = l1, let l2Node = l2 {
+            if l1Node.val <= l2Node.val {
+                cur?.next = l1Node
+                l1 = l1Node.next
+            } else {
+                cur?.next = l2Node
+                l2 = l2Node.next
+            }
+            cur = cur?.next
+        }
+        
+        cur?.next = l1 ?? l2
+        
+        return dummy.next
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof/面试题25. 合并两个排序的链表/Solution.swift

@@ -0,0 +1,33 @@
+/* public class ListNode {
+*     var val: Int
+*     var next: ListNode?
+*     init(_ val: Int) {
+*         self.val = val
+*         self.next = nil
+*     }
+* }
+*/
+
+class Solution {
+    func mergeTwoLists(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
+        let dummy = ListNode(0)
+        var cur: ListNode? = dummy
+        var l1 = l1
+        var l2 = l2
+        
+        while let l1Node = l1, let l2Node = l2 {
+            if l1Node.val <= l2Node.val {
+                cur?.next = l1Node
+                l1 = l1Node.next
+            } else {
+                cur?.next = l2Node
+                l2 = l2Node.next
+            }
+            cur = cur?.next
+        }
+        
+        cur?.next = l1 ?? l2
+        
+        return dummy.next
+    }
+}