# Merge k Sorted Lists

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

Example 1:

```Input: lists = [[1,4,5],[1,3,4],[2,6]]
Output: [1,1,2,3,4,4,5,6]
[
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`.

SOLUTION

``````public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
ListNode h = new ListNode(0);
ListNode ans=h;
while (l1 != null && l2 != null) {
if (l1.val < l2.val) {
h.next = l1;
h = h.next;
l1 = l1.next;
} else {
h.next = l2;
h = h.next;
l2 = l2.next;
}
}
if(l1==null){
h.next=l2;
}
if(l2==null){
h.next=l1;
}
return ans.next;
}
public ListNode mergeKLists(ListNode[] lists) {
if(lists.length==0){
return null;
}
int interval = 1;
while(interval<lists.length){
System.out.println(lists.length);
for (int i = 0; i + interval< lists.length; i=i+interval*2) {
lists[i]=mergeTwoLists(lists[i],lists[i+interval]);
}
interval*=2;
}

return lists[0];
}``````