Merge k Sorted Lists- Difficulty [HARD] - Time Complexity- O(N log N) and Space Complexity- O(N)

 

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 <= 10^4
• 0 <= lists[i].length <= 500
• -10^4 <= lists[i][j] <= 10^4
• lists[i] is sorted in ascending order.
• The sum of lists[i].length won't exceed 10^4.

Solution-

# Definition for singly-linked list.

# class ListNode:

#     def __init__(self, val=0, next=None):

#         self.val = val

#         self.next = next

class Solution:

    def mergeKLists(self, lists: List[Optional[ListNode]]) -> Optional[ListNode]:

        nodes=[]

        head=itr=ListNode(0) //ListNode{val: 0, next: None}

        for l in lists:

            while l:

                nodes.append(l.val)

                l=l.next

        print(nodes) //[1, 4, 5, 1, 3, 4, 2, 6]

        nodes=sorted(nodes) 

        for i in nodes:

            itr.next=ListNode(i)

            itr=itr.next

        return head.next