k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is. You may not alter the values in the nodes, only nodes itself may be changed. Only constant memory is allowed.
For example, Given this linked list: 1->2->3->4->5 For k = 2, you should return: 2->1->4->3->5 For k = 3, you should return: 3->2->1->4->5
https://leetcode.com/problems/merge-k-sorted-lists/description/ ## 题目 Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.