Leetcode 23 Merge k sorted lists Solution in Java | Hindi Coding Community

 

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 <= 104
• 0 <= lists[i].length <= 500
• -104 <= lists[i][j] <= 104
• lists[i] is sorted in ascending order.
• The sum of lists[i].length will not exceed 104.

Java Code 

public class Solution {

public ListNode mergeKLists(List<ListNode> lists) {

if (lists==null||lists.size()==0) return null;

PriorityQueue<ListNode> queue= new PriorityQueue<ListNode>(lists.size(),new Comparator<ListNode>(){

@Override

public int compare(ListNode o1,ListNode o2){

if (o1.val<o2.val)

return -1;

else if (o1.val==o2.val)

return 0;

else

return 1;

}

});

ListNode dummy = new ListNode(0);

ListNode tail=dummy;

for (ListNode node:lists)

if (node!=null)

queue.add(node);

while (!queue.isEmpty()){

tail.next=queue.poll();

tail=tail.next;

if (tail.next!=null)

queue.add(tail.next);

}

return dummy.next;

}

}