You are given an array of k linked-lists lists, each linked-list is sorted in ascending order.

*Merge all the linked-lists into one sorted linked-list and return it.*

**Example 1:**

**Input:** lists = [[1,4,5],[1,3,4],[2,6]]
**Output:** [1,1,2,3,4,4,5,6]
**Explanation:** The linked-lists are:
[
1->4->5,
1->3->4,
2->6
]
merging them into one sorted list:
1->1->2->3->4->4->5->6

**Example 2:**

**Input:** lists = []
**Output:** []

**Example 3:**

**Input:** lists = [[]]
**Output:** []

**Constraints:**

k == lists.length

0 <= k <= 10^4

0 <= lists[i].length <= 500

-10^4 <= lists[i][j] <= 10^4

lists[i] is sorted in

**ascending order**.The sum of lists[i].length won't exceed 10^4.

**Solution:**

```
class Solution {
public ListNode mergeKLists(ListNode[] lists) {
PriorityQueue<Integer> minheap = new PriorityQueue<>();
for(ListNode head:lists)
{
while(head!=null)
{
minheap.add(head.val);
head=head.next;
}
}
ListNode dummy = new ListNode(-1);
ListNode head = dummy;
while(!minheap.isEmpty())
{
head.next=new ListNode(minheap.remove());
head=head.next;
}
return dummy.next;
}
}
```

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