//2021-2-29
//剑指offer 简单
//合并两个排序的链表
public class Solution13 {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

        if (l1==null){
            return l2;
        }else if(l2==null){
            return l1;
        }
        ListNode newList = new ListNode(1);
        ListNode head = newList;
        ListNode p = l1;
        ListNode q = l2;
        while(l1!=null&& l2!=null){
            if(p.val < q.val ){
                l1 = l1.next;
                newList.next = p;
                newList = p;
                p = l1;
            }else{
                l2= l2.next;
                newList.next = q;
                newList = q;
                q = l2;
            }
        }

        if(l1 == null){
            while(l2!=null){
                l2= l2.next;
                newList.next = q;
                newList = q;
                q = l2;
            }
        }else if(l2 == null){
            while(l1!=null){
                l1 = l1.next;
                newList.next = p;
                newList = p;
                p = l1;
            }
        }
        return head;
    }
}