23.合并k个升序链表.java

import java.util.PriorityQueue;

/*
 * @lc app=leetcode.cn id=23 lang=java
 *
 * [23] 合并K个升序链表
 */

// @lc code=start
/**
 * 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) {
        if (lists.length == 0)
            return null;

        PriorityQueue<ListNode> pq = new PriorityQueue<>(lists.length, (a, b) -> a.val - b.val);
        for (int i = 0; i < lists.length; i++) {
            if (lists[i] != null) {
                pq.add(lists[i]);
            }
        }
        ListNode vNode = new ListNode(-1);
        ListNode cur = vNode;

        while (pq.peek() != null) {
            ListNode min = pq.poll();
            cur.next = min;
            cur = cur.next;

            if (min.next != null) {
                pq.add(min.next);
            }
        }
        return vNode.next;
    }
}
// @lc code=end