题解 | #合并k个已排序的链表#

1、优先队列

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
import java.util.*;
public class Solution {
    public ListNode mergeKLists(ArrayList<ListNode> lists) {
        Queue<ListNode> queue = new PriorityQueue<>((a, b) -> a.val - b.val);
        if (lists == null || lists.size() == 0) return null;
        for (ListNode head : lists) {
            if (head == null) continue;
            queue.offer(head);
        }
        ListNode dummy = new ListNode(0);
        ListNode head = dummy;
        while (!queue.isEmpty()) {
            ListNode cur = queue.poll();
            head.next = cur;
            head = head.next;
            if (cur.next != null) {
                queue.offer(cur.next);
            }
        }
        return dummy.next;
    }
}