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74--merge-k-sorted-lists.java
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74--merge-k-sorted-lists.java
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/**
* 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) {
PriorityQueue<ListNode> pq = new PriorityQueue(new Comparator<ListNode>() {
@Override
public int compare(ListNode node1, ListNode node2) {
return node1.val - node2.val;
}
});
for (ListNode head : lists) {
if (head != null) {
pq.add(head);
}
}
ListNode head = new ListNode(-1);
ListNode curr = head;
while (!pq.isEmpty()) {
ListNode tmp = pq.poll();
curr.next = tmp;
curr = tmp;
if (curr.next != null) {
pq.add(curr.next);
}
}
return head.next;
}
}
// TC: O(n * log k) SC: O(k)