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.

归并两个有序链表，此题看完你应该去看看算法中的归并排序是如何实现的

/** * 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 l3=new ListNode(0);ListNode head=l3;while(l1!=null||l2!=null){if(l1==null){l3.next=l2;break;}if(l2==null){l3.next=l1;break;}if(l1.val<l2.val){l3.next=l1;l1=l1.next;}else{l3.next=l2;l2=l2.next ;}l3=l3.next;}return head.next;    }}