• 常规
/**
 * 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) {
        if(l1==null)
            return l2;
        if(l2 ==null)
            return l1;
        ListNode newList = null;

        if(l1.val>l2.val){
            newList = l2;
            newList.next = mergeTwoLists(l1,l2.next);
        }
        else{
            newList = l1;
            newList.next = mergeTwoLists(l1.next,l2);
        }
        return newList;
    }
}
  • 参考
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
    if (l1 == null) return l2;
    if (l2 == null) return l1;
    if (l1.val < l2.val) {
        l1.next = mergeTwoLists(l1.next, l2);
        return l1;
    } else {
        l2.next = mergeTwoLists(l1, l2.next);
        return l2;
    }
}