21. Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

此题考查链表的操作，比较简单，直接上代码：

/**

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode(int x) { val = x; }

 * }

 */

public class Solution {

    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

        ListNode head = new ListNode(0);

        ListNode dummy = head;

        while(l1!=null&&l2!=null){

            if(l1.val<l2.val){

                ListNode node = new ListNode(l1.val);

                l1 = l1.next;

                head.next = node;

                head = head.next;

            }else{

                ListNode node = new ListNode(l2.val);

                l2 = l2.next;

                head.next = node;

                head = head.next;

            }

        }

        if(l1!=null){

            ListNode node = l1;

            head.next = node;

        }

        if(l2!=null){

            ListNode node = l2;

            head.next = node;

        }

        return dummy.next;

    }

}