[leetcode]合并两个有序链表题解

题目描述

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]

示例 2：

输入：l1 = [], l2 = []
输出：[]

示例 3：

输入：l1 = [], l2 = [0]
输出：[0]

 

提示：

• 两个链表的节点数目范围是 [0, 50]
• -100 <= Node.val <= 100
• l1 和 l2 均按 非递减顺序 排列

解决方案

package leetcode.editor.cn;

/**
 * 合并两个有序链表
 *
 * @author 沙漠渔
 * @date 2022-01-25 12:06:35
 */
public class 合并两个有序链表 {
    static
//leetcode submit region begin(Prohibit modification and deletion)
    class Solution {
        public 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(list2.next, list1);
                return list2;
            }
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

    static class ListNode {
        int val;
        ListNode next;

        public ListNode(int val) {
            this.val = val;
        }

        public ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }

    /**
     * 最终测试主方法
     */
    public static void main(String[] args) {
        Solution solution = new Solution();
        ListNode list1 = new ListNode(1, new ListNode(2, new ListNode(4)));
        ListNode list2 = new ListNode(1, new ListNode(3, new ListNode(4)));
        ListNode listNode = solution.mergeTwoLists(list1, list2);
        for (ListNode i = listNode; i != null; i = i.next) {
            if (i.next == null) {
                System.out.println(i.val + " ");
            } else {
                System.out.print(i.val + " ");
            }
        }
    }
}