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
        if(lists == null || lists.size() == 0) return null;
        //小顶堆
        PriorityQueue<ListNode> minHeap = new PriorityQueue<>((a,b) -> a.val - b.val);
        //将所有节点放入小顶堆
        for(ListNode head : lists){
            if(head != null )
            minHeap.offer(head);
        }

        ListNode dummy = new ListNode(0);
        ListNode curr = dummy;
        //逐步取出最小的节点
        while(!minHeap.isEmpty()){
            ListNode minNode = minHeap.poll();
            curr.next = minNode;
            curr = curr.next;
        //如果取出的节点后续还有节点，将后续的节点继续放入堆中
            if(minNode.next != null){
                minHeap.offer(minNode.next);
            }
        }
        return dummy.next;
    }
}