23. 合并K个升序链表

ゝ一纸荒年。 2022-09-09 00:26 194阅读 0赞

[https://leetcode-cn.com/problems/merge-k-sorted-lists/submissions/][https_leetcode-cn.com_problems_merge-k-sorted-lists_submissions]

难度困难1477

给你一个链表数组，每个链表都已经按升序排列。

请你将所有链表合并到一个升序链表中，返回合并后的链表。

**示例 1：**

输入：lists = [[1,4,5],[1,3,4],[2,6]]
    输出：[1,1,2,3,4,4,5,6]
    解释：链表数组如下：
    [
      1->4->5,
      1->3->4,
      2->6
    ]
    将它们合并到一个有序链表中得到。
    1->1->2->3->4->4->5->6

**示例 2：**

输入：lists = []
    输出：[]

**示例 3：**

输入：lists = [[]]
    输出：[]

**提示：**

*  `k == lists.length`
 *  `0 <= k <= 10^4`
 *  `0 <= lists[i].length <= 500`
 *  `-10^4 <= lists[i][j] <= 10^4`
 *  `lists[i]` 按 **升序** 排列
 *  `lists[i].length` 的总和不超过 `10^4`

通过次数308,052提交次数551,571

/**
     * Definition for singly-linked list.
     * public class ListNode {
     *     int val;
     *     ListNode next;
     *     ListNode() {}
     *     ListNode(int val) { this.val = val; }
     *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
     * }
     */
    class Solution {
        public ListNode mergeKLists(ListNode[] lists) {
            ListNode h = null;
            if(lists.length == 0) return h;
            List<Integer> ans = new ArrayList<Integer>();
            for(int i=0;i<lists.length;i++)
            {
                ListNode head = lists[i];
                while(head!=null)
                {
                    ans.add(head.val);
                    head = head.next;
                }
            }
            if(ans.size()==0) return h;
            Collections.sort(ans);
            ListNode head = new ListNode();
            ListNode a = new ListNode();
            head.next = a;
            for(int i=0;i<ans.size();i++)
            {
                a.val = ans.get(i);
                if(i+1 == ans.size()) break;
                a.next = new ListNode();
                a = a.next;
            }
            return head.next;
        }
    }

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[https_leetcode-cn.com_problems_merge-k-sorted-lists_submissions]: https://leetcode-cn.com/problems/merge-k-sorted-lists/submissions/
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA5Yqq5Yqb5a2m5Lmg55qE5qKF5a2Q_size_14_color_FFFFFF_t_70_g_se_x_16]: /images/20220829/ec94805490c9427b9b08b712a30b2478.png