23. 合并K个排序链表

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeKLists(ListNode[] lists) {
         PriorityQueue<ListNode> pq = new PriorityQueue<>(new Comparator<ListNode>() {
            public int compare(ListNode a, ListNode b) {
                return a.val-b.val;
            }
        });
        ListNode ret = null, cur = null;
        for(ListNode node: lists) {
            if(null != node) {
                pq.add(node);    
            }
        }
        while(!pq.isEmpty()) {
            ListNode node = pq.poll();
            if(null == ret) {
                ret = cur = node;
            }
            else {
                cur = cur.next = node;
            }
            if(null != node.next) {
                pq.add(node.next);    
            }
        }
        return ret;
    }
}

思路：最小堆 java提供了该模块