剑指offer 合并两个排序的链表

public class Solution {
    public ListNode Merge(ListNode list1,ListNode list2) {
        ListNode head;
        if(list1==null){
            return list2;
        }
        if(list2==null){
            return list1;
        }
        if(list1.val < list2.val){
            head=list1;
            head.next=Merge(list1.next,list2);
        }else{
            head=list2;
            head.next=Merge(list1,list2.next);
        }
        return head;
    }
}