import java.util.ArrayList;

import java.util.List;

public class ListNode {

int val;

ListNode next;

ListNode() {}

ListNode(int val) {

this.val = val;

}

ListNode(int val, ListNode next) {

this.val = val;

this.next = next;

}

public static ListNode numToList(int[] nums) {

ListNode dummy = new ListNode(-1);

ListNode curr = dummy;

for(int n: nums) {

curr.next = new ListNode(n);

curr = curr.next;

}

return dummy.next;

}

public static List<Integer> listToArrayList(ListNode head) {

List<Integer> arr = new ArrayList<Integer>();

while (head!=null) {

arr.add(head.val);

head = head.next;

}

return arr;

}

public static ListNode merge(ListNode l1, ListNode l2) {

ListNode dummy = new ListNode(-1);

ListNode curr = dummy;

while (l1!=null) {

curr.next = l1;

curr = curr.next;

l1 = l1.next;

}

while (l2!=null) {

curr.next = l2;

curr = curr.next;

l2 = l2.next;

}

return dummy.next;

}

}