[LeetCode23] 合并 K个有序链表

package com.wangxiaohu;

import java.util.PriorityQueue;

public class LeetCode23 {

    
    public ListNode mergeKLists(ListNode[] lists) {
        if (lists.length == 0) {
            return null;
        }

        // 虚拟头结点
        ListNode dummy = new ListNode(-1);
        ListNode p = dummy;
        // // 优先级队列，最小堆
        PriorityQueue pq = new PriorityQueue<>(
                lists.length, (a, b) -> (a.val - b.val));

        // 将 k 个链表的头结点加入最小堆
        for (ListNode head : lists) {
            if (head != null)
                pq.add(head);
        }

        while (!pq.isEmpty()) {
            // 获取最小节点，接到结果链表中
            ListNode node = pq.poll();
            p.next = node;
            if (node.next != null) {
                pq.add(node.next);
            }
            // p 指针不断前进
            p = p.next;
        }
        return dummy.next;
    }

    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;
        }
    }
}