feat: add swift implementation to lcof2 problem: No.077 (doocs#3456)

Author: klever34

lcof2/剑指 Offer II 077. 链表排序/README.md

@@ -377,6 +377,64 @@ public class Solution {
 }
 ```
 
+#### Swift
+
+```swift
+
+/** class ListNode {
+*    var val: Int
+*    var next: ListNode?
+*    init() { self.val = 0; self.next = nil }
+*    init(_ val: Int) { self.val = val; self.next = nil }
+*    init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next }
+* }
+*/
+
+class Solution {
+    func sortList(_ head: ListNode?) -> ListNode? {
+        guard let head = head, head.next != nil else {
+            return head
+        }
+        
+        var slow: ListNode? = head
+        var fast: ListNode? = head.next
+        
+        while fast != nil && fast?.next != nil {
+            slow = slow?.next
+            fast = fast?.next?.next
+        }
+        
+        let mid = slow?.next
+        slow?.next = nil
+        
+        let left = sortList(head)
+        let right = sortList(mid)
+        
+        return merge(left, right)
+    }
+    
+    private func merge(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
+        let dummy = ListNode()
+        var cur = dummy
+        var l1 = l1, l2 = l2
+        
+        while let node1 = l1, let node2 = l2 {
+            if node1.val <= node2.val {
+                cur.next = node1
+                l1 = node1.next
+            } else {
+                cur.next = node2
+                l2 = node2.next
+            }
+            cur = cur.next!
+        }
+        
+        cur.next = l1 ?? l2
+        return dummy.next
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 077. 链表排序/Solution.swift

@@ -0,0 +1,53 @@
+
+/** class ListNode {
+*    var val: Int
+*    var next: ListNode?
+*    init() { self.val = 0; self.next = nil }
+*    init(_ val: Int) { self.val = val; self.next = nil }
+*    init(_ val: Int, _ next: ListNode?) { self.val = val; self.next = next }
+* }
+*/
+
+class Solution {
+    func sortList(_ head: ListNode?) -> ListNode? {
+        guard let head = head, head.next != nil else {
+            return head
+        }
+        
+        var slow: ListNode? = head
+        var fast: ListNode? = head.next
+        
+        while fast != nil && fast?.next != nil {
+            slow = slow?.next
+            fast = fast?.next?.next
+        }
+        
+        let mid = slow?.next
+        slow?.next = nil
+        
+        let left = sortList(head)
+        let right = sortList(mid)
+        
+        return merge(left, right)
+    }
+    
+    private func merge(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
+        let dummy = ListNode()
+        var cur = dummy
+        var l1 = l1, l2 = l2
+        
+        while let node1 = l1, let node2 = l2 {
+            if node1.val <= node2.val {
+                cur.next = node1
+                l1 = node1.next
+            } else {
+                cur.next = node2
+                l2 = node2.next
+            }
+            cur = cur.next!
+        }
+        
+        cur.next = l1 ?? l2
+        return dummy.next
+    }
+}