原题地址：https://oj.leetcode.com/problems/merge-k-sorted-lists/
题意：Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
解题思路：归并k个已经排好序的链表。使用堆这一数据结构，首先将每条链表的头节点进入堆中，然后将最小的弹出，并将最小的节点这条链表的下一个节点入堆，依次类推，最终形成的链表就是归并好的链表。
代码：
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: # @param a list of ListNode # @return a ListNode def mergeKLists(self, lists): heap = [] for node in lists: if node: heap.append((node.val, node)) heapq.heapify(heap) head = ListNode(0); curr = head while heap: pop = heapq.heappop(heap) curr.next = ListNode(pop[0]) curr = curr.next if pop[1].next: heapq.heappush(heap, (pop[1].next.val, pop[1].next)) return head.next