LeetCode No.21 MergeTwoSortedLists

/**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.Subscribe to see which companies asked this question.*//** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { val = x; } * } */public class Solution {    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {        if(l1 == null) return l2;        if(l2 == null) return l1;        ListNode mergeHead;        if(l1.val < l2.val){            mergeHead = l1;            mergeHead.next = mergeTwoLists(l1.next, l2);        }        else{            mergeHead = l2;            mergeHead.next = mergeTwoLists(l1, l2.next);        }        return mergeHead;    }}