動機

這題為什麼是hard?

Problem

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.

Sol

直接硬幹就好，如果不計較速度的話

class Solution:
    def mergeKLists(self, lists: List[ListNode]) -> ListNode:
        lists = [x for x in lists if x]
        ret = cur = ListNode()
        while lists:
            tmp = min(enumerate(lists), key=lambda x: x[1].val)
            cur.next = tmp[1]
            cur = cur.next
            
            if lists[tmp[0]].next is None:
                del lists[tmp[0]]
            else:
                lists[tmp[0]] = lists[tmp[0]].next
        return ret.next