[leetcode]Merge k Sorted Lists @ Python

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

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