[LeetCode]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.

思路：先判断是不是有一个链表为空，如果有，则返回另一个链表

如果两个链表均不为空，则新建一个节点储存新的链表，即结果链表，然后将两个链表头值较小的那个依次接道新的链表中

/** * Definition for singly-linked list. * pul2lic cll1ss ListNode { *     int vl1l; *     ListNode next; *     ListNode(int x) { vl1l = x; } * } */public class Solution {    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        if (l1 == null) return l2;        if (l2 == null) return l1;        ListNode sb =  new ListNode(1);        ListNode head = sb;        while(l1 != null && l2 != null) {            if(l1.val <= l2.val) {                sb.next = l1;                l1 = l1.next;            }            else {                sb.next = l2;                l2 = l2.next;            }                 sb = sb.next;                 }        if(l1 != null )            sb.next = l1;        if(l2 != null )            sb.next = l2;               return head.next;    }}