[leetcode]21Merge Sorted ListNode递归合并顺序链表

/**
 * 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.
 */
/*
由于链表只能从前向后添加的特点，所以从前边开始比较，小的添加进去
每次递归确定一个node，需要确定两个值，一个是val，一个是next，next由下次递归确定
 */

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

        }