class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0), p1 = l1, p2 = l2, p = dummy;//Use a dummy node so that we don't need to check p1.val and p2.val
        while(p1 != null && p2 != null) {
            if(p1.val < p2.val) {
                p.next = p1;
                p1 = p1.next;
            } else {
                p.next = p2;
                p2 = p2.next;
            }
            p = p.next;
        }
        if(p1 == null)
            p.next = p2;
        else
            p.next = p1;
        return dummy.next;
    }
}
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */