题解 | 合并k个已排序的链表

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param lists ListNode类ArrayList 
     * @return ListNode类
     */
    public ListNode mergeKLists (ArrayList<ListNode> lists) {
        // write code here
        PriorityQueue<ListNode> pq = new PriorityQueue<>((a,b)->a.val-b.val);
        for(ListNode list : lists){
            if(list!=null){
                pq.offer(list);
            }
        }
        ListNode dummy = new ListNode(-1);
        ListNode cur = dummy;
        while(!pq.isEmpty()){
            ListNode node = pq.poll();
            if(node.next!=null){
                pq.offer(node.next);
            }
            cur.next=node;
            cur=cur.next;
        }
        return dummy.next;

    }
}