feat: add Swift codes for hash_algorithm article (#576)

codes/swift/utils/ListNode.swift

@@ -4,7 +4,7 @@
  * Author: nuomi1 (nuomi1@qq.com)
  */
 
-public class ListNode {
+public class ListNode: Hashable {
     public var val: Int // 节点值
     public var next: ListNode? // 后继节点引用
 
@@ -12,6 +12,15 @@ public class ListNode {
         val = x
     }
 
+    public static func == (lhs: ListNode, rhs: ListNode) -> Bool {
+        lhs.val == rhs.val && lhs.next.map { ObjectIdentifier($0) } == rhs.next.map { ObjectIdentifier($0) }
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(val)
+        hasher.combine(next.map { ObjectIdentifier($0) })
+    }
+
     public static func arrToLinkedList(arr: [Int]) -> ListNode? {
         let dum = ListNode(x: 0)
         var head: ListNode? = dum