/** * Definition for singly-linked 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; } * } */class Solution {    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        ListNode root=new ListNode(0);        ListNode head=root;        while(l1!=null && l2!=null){            if(l1.val<l2.val){                head.next=l1;                head=head.next;                l1=l1.next;            }else{                head.next=l2;                head=head.next;                l2=l2.next;            }        }        if(l1==null){            head.next=l2;        }        if(l2==null){            head.next=l1;        }        return root.next;    }}