描述

合并 k 个升序的链表并将结果作为一个升序的链表返回其头节点。

数据范围：节点总数 0≤𝑛≤50000≤n≤5000，每个节点的val满足 ∣𝑣𝑎𝑙∣<=1000∣val∣<=1000

要求：时间复杂度 𝑂(𝑛𝑙𝑜𝑔𝑛)O(nlogn)

示例1

示例1

输入： [{1,2,3},{4,5,6,7}]
输出： {1,2,3,4,5,6,7}

示例2

输入：[{1,2},{1,4,5},{6}]
返回值：{1,1,2,4,5,6}

思路：

需要借助BM4写的代码，看我上一篇博客。然后从左向右每两个链表之间一一合并，得到最终结果。

package com.niuke;import java.util.ArrayList;public class BM5 {public ListNode mergeKLists(ArrayList<ListNode> lists) {//看学习通if (lists == null || lists.size()==0) return null;if (lists.size() == 1) return lists.get(0);ListNode newHead = lists.get(0);for (int i = 1; i < lists.size(); i++) {newHead = Merge(newHead,lists.get(i));}return newHead;}private ListNode Merge(ListNode pHead1, ListNode pHead2) {ListNode cur = new ListNode(0);ListNode dummy = cur;while (pHead1 != null && pHead2 != null) {//找到其中比较小的那个if (pHead1.val < pHead2.val) {cur.next = pHead1;pHead1 = pHead1.next;cur = cur.next;} else {cur.next = pHead2;pHead2 = pHead2.next;cur = cur.next;}}cur.next = pHead1 != null ? pHead1 : pHead2;return dummy.next;}static class ListNode {int val;ListNode next = null;public ListNode(int val) {this.val = val;}}
}