Merge k sorted linked lists

Merge k sorted linked lists and return it as one sorted list.

每个列表都已经是有序的 所以本质上是对有k个元素的数组进行排序（且数组内的元素需要变化

heapq 为python的一个实现最小堆的库

# T(nlogn) S(n)
import heapq
class Solution:
    def mergeKLists(self, lists):
        heap = []
        for l in lists:
            while l:
                heapq.heappush(heap, l.val)
                l = l.next
        head = ListNode(val=None)
        cur = head
        while len(heap) != 0:
            cur.next = ListNode(heapq.heappop(heap))
            cur = cur.next
        return head.next