23. Merge k Sorted Lists

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: []

讀到陣列排序後丟回去。

Time: O(n), Space: O(n)

# 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):
        """
        :type lists: List[ListNode]
        :rtype: ListNode
        """
        res = []
        for x in lists:
            while x:
                res.append(x.val)
                x=x.next
                
        if not res: return
        
        # sort the result list
        res = sorted(res)
        
        # push all the values from the list to the final linked list
        head = ListNode(res[0])
        node = head
        for x in res[1:]:
            node.next = ListNode(x)
            node = node.next
        return head

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