[Java] Daily LeetCode Challenge 23. Merge k Sorted Lists

https://leetcode.com/problems/merge-k-sorted-lists/

Merge k Sorted Lists - LeetCode

 

LinkedList 값 받아오면서 null값만 적절히 체크해주면 금방 풀리는 문제

LeetCode에는 리스트 관련 문제들이 많은 듯 하다

 

 

[코드]

/**
 * 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<Integer> pq = new PriorityQueue<>(Collections.reverseOrder());

        for(int i=0; i<lists.length; i++){
            ListNode node = lists[i];

            while(node != null){
                pq.add(node.val);
                node = node.next;
            }
        }

        if(pq.size() == 0)
            return null;

        ListNode node = new ListNode(pq.poll());
        while(!pq.isEmpty()){
            ListNode now = new ListNode(pq.poll(), node);
            node = now;
        }

        return node;
    }
}