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.

题意:合并两个有序的链表,并返回新的链表。

思路：使用双指针，分别指向两个链表，然后比较大小依次加入新的链表，最后将不为空的链表加入到新的链表尾部。

代码：

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {            ListNode p1= l1;             ListNode p2= l2;                          ListNode fakeHead = new ListNode(0);             ListNode p = fakeHead;             while(p1!=null && p2!=null){                 if(p1.val <= p2.val){                     p.next = p1;                     p1 = p1.next;                 }else{                     p.next = p2;                     p2 = p2.next;                 }                 p = p.next;             }             if(p1!=null) p.next = p1;             if(p2!=null) p.next = p2;                     return fakeHead.next;    }