Merge k Sorted Lists

Merge k sorted linked lists and return it as one sorted list.
Analyze and describe its complexity.

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Yes

Example

Given lists:

[
2->4->null,
null,
-1->null
],

return 

-1->2->4->null

.
K路归并算法，使用heap的方式处理

/**
* Definition for ListNode.
* public class ListNode {
*     int val;
*     ListNode next;
*     ListNode(int val) {
*         this.val = val;
*         this.next = null;
*     }
* }
*/
public class Solution {
/**
* @param lists: a list of ListNode
* @return: The head of one sorted list.
*/
public ListNode mergeKLists(List<ListNode> lists) {
// write your code here
if (lists == null || lists.size() == 0) {
return null;
}
ListNode dummy = new ListNode(0);
ListNode head = dummy;
Comparator<ListNode> cmp = new Comparator<ListNode>() {
public int compare(ListNode a, ListNode b) {
return a.val - b.val;
}
};
PriorityQueue<ListNode> heap = new PriorityQueue<>(10, cmp);
for (int i = 0; i < lists.size(); i++) {
ListNode node =  lists.get(i);
while (node != null) {
heap.offer(node);
node = node.next;
}
}
while (!heap.isEmpty()) {
head.next = heap.poll();
head = head.next;
}
return dummy.next;
}
}