[Solved] 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.

Question

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.

Python Solution

from heapq import heappop,heappush,heapify

class Solution:
    def mergeKLists(self, lists: List[ListNode]) -> ListNode:
        h = []
        
        for l in lists:
            while l:
                heappush(h,l.val)
                l = l.next
        
        head = ListNode(0)
        head1 = head
        
        while h:
            head.next = ListNode(heappop(h))
            head = head.next
        
        return head1.next