【算法hot-21】合并链表

合并链表

将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

示例 1：

输入：l1 = [1,2,4], l2 = [1,3,4]
输出：[1,1,2,3,4,4]

public class LC003_21_mergeTwoLists_01 {

    public static void main(String[] args) {
        ListNode node = mergeTwoLists(ListNode.createLink(), ListNode.createLink());
        ListNode.printLink(node);
    }

    public static ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        if (list1 == null) {
            return list2;
        }
        if (list2 == null) {
            return list1;
        }
        if (list1.val < list2.val) {
            list1.next = mergeTwoLists(list1.next, list2);
            return list1;
        } else {
            list2.next = mergeTwoLists(list1, list2.next);
            return list2;
        }
    }
}

//迭代
public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode l3 = new ListNode(-1);
        ListNode l4 = l3;
        while (l1 != null && l2 != null) {
            if (l1.val > l2.val) {
                l4.next = l2;
                l2 = l2.next;
            } else {
                l4.next = l1;
                l1 = l1.next;
            }
            l4 = l4.next;
        }
        l4.next = l1 == null ? l2 : l1;
        return l3.next;
    }