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合并 K 个升序链表

Merge k Sorted Lists

专题
Algorithmic Programming / 算法编程
难度
L4
来源
Citadel

题目详情

问题：合并 K 个升序链表

考察：链表、贪心、数组

来源：Citadel

链接：https://www.jointaro.com/interviews/questions/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 linked 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.
解析

思路：把每个链表头放入按节点值排序的小根堆，每次弹出最小节点接到结果链表，并把它的下一个节点入堆。

复杂度：设总节点数 N，链表数 k，时间 O(N log k)，空间 O(k)。