Leetcode 21 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.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

1)

/**
 * 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) {
        ListNode node = new ListNode(-1);
        ListNode list = new ListNode(-1);
        list = node;
        while(l1 != null && l2 != null){
            if(l1.val <= l2.val){
                node.next = l1;
                l1 = l1.next;
            }else if(l2.val < l1.val){
                node.next = l2;
                l2 = l2.next;
            }
            node = node.next;
        }
        if(l1 != null){
            node.next = l1;
        }else if(l2 != null){
            node.next = l2;
        }
        return list.next;
    }
}

2)

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;
		}
}

使用了遞迴的方法