LeetCode97|合并两个有序链表

示例：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class MergeTwoListsTest {
    public static void main(String[] args) {
        ListNode l11 = new ListNode(1);
        ListNode l12 = new ListNode(2);
        ListNode l13 = new ListNode(4);
        l11.next = l12;
        l12.next = l13;

        ListNode l21 = new ListNode(1);
        ListNode l22 = new ListNode(3);
        ListNode l23 = new ListNode(4);
        l21.next = l22;
        l22.next = l23;
        ListNode listNode = mergeTwoLists2(l11, l21);
        System.out.println("listNode = " + listNode);


    }

    public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        ListNode dummyNode = new ListNode(-1);
        ListNode temp = dummyNode;
        while (l1 != null && l2 != null) {
            if (l1.val <= l2.val) {
                temp.next = l1;
                l1 = l1.next;
            } else {
                temp.next = l2;
                l2 = l2.next;
            }
            temp = temp.next;
        }
        temp.next = l1 == null ? l2 : l1;
        return dummyNode.next;
    }

    public static ListNode mergeTwoLists2(ListNode l1, ListNode l2) {
        if (l1 == null) {
            return l2;
        }
        if (l2 == null) {
            return l1;
        }
        List<Integer> list = new ArrayList<>();
        while (l1 != null) {
            list.add(l1.val);
            l1 = l1.next;
        }
        while (l2 != null) {
            list.add(l2.val);
            l2 = l2.next;
        }
        ListNode dummyNode = new ListNode(-1);
        ListNode tempNode = dummyNode;

        Collections.sort(list);
        for (Integer num : list
        ) {
            tempNode.next = new ListNode(num);
            tempNode = tempNode.next;
        }

        return dummyNode.next;
    }
}