21. Merge Two Sorted Lists

21. Merge Two Sorted Lists.swift

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public var val: Int
 *     public var next: ListNode?
 *     public init(_ val: Int) {
 *         self.val = val
 *         self.next = nil
 *     }
 * }
 */
class Solution {
    func mergeTwoLists(_ l1: ListNode?, _ l2: ListNode?) -> ListNode? {
        var l1 = l1
        var l2 = l2
        var arr: [Int] = []
        
        while l1 != nil {
            arr.append(l1?.val ?? -1)
            
            l1 = l1?.next
        }
        
        while l2 != nil {
            arr.append(l2?.val ?? -1)
            
            l2 = l2?.next
        }
        guard arr.isEmpty != true else {
            return nil
        }
        arr = arr.sorted()
        
        var resNode: ListNode? = ListNode(arr[0])
        
        var currentNode = resNode
        
        for idx in 1 ..< arr.count {
            currentNode?.next = ListNode(arr[idx])
            currentNode = currentNode?.next
        }
        
        return resNode 
    }
}