1class Solution {2    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {3        ListNode dummy = new ListNode(0), tail = dummy;4        while (list1 != null && list2 != null) {5            if (list1.val <= list2.val) {6                tail.next = list1;7                list1 = list1.next;8            } else {9                tail.next = list2;10                list2 = list2.next;11            }12            tail = tail.next;13        }14        tail.next = list1 == null ? list2 : list1;15        return dummy.next;16    }17}