Swift implementation for LCOF2 022

Author: klever34

lcof2/剑指 Offer II 022. 链表中环的入口节点/README.md

@@ -271,4 +271,40 @@ var detectCycle = function (head) {
 };
 ```
 
+#### Swift
+
+```swift
+/* class ListNode {
+*     var val: Int
+*     var next: ListNode?
+*     init(_ val: Int) {
+*         self.val = val
+*         self.next = nil
+*     }
+* }
+*/
+
+class Solution {
+    func detectCycle(_ head: ListNode?) -> ListNode? {
+        var fast = head
+        var slow = head
+        
+        while fast != nil && fast?.next != nil {
+            slow = slow?.next
+            fast = fast?.next?.next
+            
+            if slow === fast {
+                var ans = head
+                while ans !== slow {
+                    ans = ans?.next
+                    slow = slow?.next
+                }
+                return ans
+            }
+        }
+        return nil
+    }
+}
+```
+
 <!-- problem:end -->

lcof2/剑指 Offer II 022. 链表中环的入口节点/Solution.swift

@@ -0,0 +1,31 @@
+/* class ListNode {
+*     var val: Int
+*     var next: ListNode?
+*     init(_ val: Int) {
+*         self.val = val
+*         self.next = nil
+*     }
+* }
+*/
+
+class Solution {
+    func detectCycle(_ head: ListNode?) -> ListNode? {
+        var fast = head
+        var slow = head
+        
+        while fast != nil && fast?.next != nil {
+            slow = slow?.next
+            fast = fast?.next?.next
+            
+            if slow === fast {
+                var ans = head
+                while ans !== slow {
+                    ans = ans?.next
+                    slow = slow?.next
+                }
+                return ans
+            }
+        }
+        return nil
+    }
+}