剑指 Offer 25. 合并两个排序的链表

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        //判空
        if(l1 == null){
            return l2;
        }
        if(l2 == null){
            return l1;
        }
        //定义合并之后的链表lMerge 
        ListNode lMerge = null;
        //合并时，l1和l2 那个小，就将小的节点赋给lMerge,如此递归下去
        if(l1.val < l2.val){
            lMerge = l1 ;
            lMerge.next = mergeTwoLists(l1.next,l2);
        }
        else
        {
            lMerge = l2;
            lMerge.next = mergeTwoLists(l1,l2.next);
        }
        return lMerge;
    }
}