题目链接

思路

使用优先队列，先把每个链表的头加入队列。然后每次出队列，都把出来的节点向后移动，直到尾。

代码

import java.util.*
import kotlin.Comparator
class Solution {
    fun mergeKLists(lists: Array<ListNode?>): ListNode? {
        val queue = PriorityQueue<ListNode>(Comparator<ListNode>{ o1, o2->
            o1.`val` - o2.`val`
        })
        if (lists.isEmpty()) return null
        for (i in lists.indices) {
            if (lists[i] != null) queue.add(lists[i])
            lists[i] = lists[i]?.next
        }
        val head = ListNode(0)
        var curr = head
        while (queue.isNotEmpty()) {
            val nowNode = queue.poll()
            curr.next = nowNode
            curr = curr.next!!
            if (nowNode.next != null) {
                queue.add(nowNode.next)
            }
        }
        return head.next
    }
}