合并K个升序链表

力扣链接：合并K个升序链表

package com.harrison.class06;

import java.util.Comparator;
import java.util.List;
import java.util.PriorityQueue;


public class Code06_MergeKSortedLists {
    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;
        }
    }

    public static ListNode mergeKLists(ListNode[] lists) {
        if (lists == null) {
            return null;
        }
        PriorityQueue heap = new PriorityQueue<>(new ListNodeComparator());
        for (int i = 0; i < lists.length; i++) {
            if(lists[i]!=null){
                heap.add(lists[i]);
            }
        }
        if (heap.isEmpty()) {
            return null;
        }
        ListNode head = heap.poll();
        ListNode pre = head;
        if (pre.next != null) {
            heap.add(pre.next);
        }
        while(!heap.isEmpty()){
            ListNode cur=heap.poll();
            pre.next=cur;
            pre=cur;
            if(cur.next!=null){
                heap.add(cur.next);
            }
        }
        return head;
    }

    public static class ListNodeComparator implements Comparator {
        public int compare(ListNode o1, ListNode o2) {
            return o1.val - o2.val;
        }
    }
}