[leetcode] Merge k sorted lists

Almost forget the properties of Link list

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public class Solution { public ListNode mergeKLists(ListNode[] lists) { if (lists == null || lists.length == 0) return null; PriorityQueue<ListNode> queue = new PriorityQueue<ListNode>(lists.length, new Comparator<ListNode>(){ public int compare(ListNode n1, ListNode n2){ return n1.val-n2.val; } }); for (int i = 0; i < lists.length; i++){ if (lists[i] != null){ queue.add(lists[i]); } } ListNode dummy = new ListNode(-1); ListNode previous = dummy; while (!queue.isEmpty()){ ListNode temp = queue.poll(); previous.next = temp; if (temp.next != null){ queue.add(temp.next); } previous = previous.next; } return dummy.next; } }