LeetCode 21 - Merge Two Sorted Lists

https://leetcode.com/problems/merge-two-sorted-lists/ 

package LeetCode;

public class LeetCode21 {

    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;
        }
    }
     
    class Solution {
        public ListNode mergeTwoLists(ListNode list1, ListNode list2) {

            ListNode ans = new ListNode(-1);
            ListNode list = ans;

            while (list1 != null && list2 != null) {
                if (list1.val < list2.val) {
                    list.next = list1;
                    list1 = list1.next;
                } else {
                    list.next = list2;
                    list2 = list2.next;
                }

                list = list.next;

            }

            list.next = list1 == null ? list2 : list1;

            return ans.next;
        }
    }
}