Linked List in place merged of two sorted lists

MergeSortedLinkedList.swift

import UIKit
import PlaygroundSupport

class Node {
  var data: Int
  var next: Node?
  
  init(data: Int) {
    self.data = data
  }
}

class LinkedList {
  var head: Node?
  
  init(head: Node?) {
    self.head = head
  }
  
  func printList() {
    print("list is: ")
    var node: Node? = head
    while let current = node {
      print(current.data)
      node = current.next
    }
  }
  
  static func mergeList(ll1: LinkedList?, ll2: LinkedList?) -> LinkedList? {
    var h1 = ll1?.head
    var h2 = ll2?.head
    
    guard h1 != nil else {
      return LinkedList(head: h2)
    }
    guard h2 != nil else {
      return LinkedList(head: h1)
    }
    
    let head: Node?
    var prev: Node?
    
    if (h1?.data ?? 0) < (h2?.data ?? 0) {
      head = h1
      h1 = h1?.next
    } else {
      head = h2
      h2 = h2?.next
    }
    prev = head
    
    while h1 != nil && h2 != nil {
      if (h1?.data ?? 0) < (h2?.data ?? 0) {
        prev?.next = h1
        prev = h1
        h1 = h1?.next
      } else {
        prev?.next = h2
        prev = h2
        h2 = h2?.next
      }

      if h1 == nil {
        prev?.next = h2
      }
      if h2 == nil {
        prev?.next = h1
      }
    }
    return LinkedList(head: head)
  }
}

let node1 = Node(data: 1)
let node3 = Node(data: 3)
let node5 = Node(data: 5)

node1.next = node3
node3.next = node5
let ll1 = LinkedList(head: node1)
ll1.printList()

let node2 = Node(data: 2)
let node4 = Node(data: 4)
let node7 = Node(data: 7)
let node10 = Node(data: 10)

node2.next = node4
node4.next = node7
node7.next = node10
let ll2 = LinkedList(head: node2)
ll2.printList()

let mergedList = LinkedList.mergeList(ll1: ll1, ll2: ll2)
mergedList?.printList()