两个有序链表的合并

两个有序链表的合并，最开始我想的是两个有序数组的合并。

一、迭代版

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode head = new ListNode(-1);
        ListNode cur = head;
        while(l1 != null && l2 != null){
            if (l1.val < l2.val) {
                cur.next = l1;
                l1 = l1.next;
            } else {
                cur.next = l2;
                l2 = l2.next;
            }
            cur = cur.next;
        }
        if (l1 != null) {
            cur.next = l1;
        } 
        if (l2 != null) {
            cur.next = l2;
        }      
        return head.next;
    }