Leetcode 23 Merge k Sorted Lists

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @param {ListNode[]} lists
    # @return {ListNode}
    def mergeKLists(self, lists):
        
        heap = []
        for node in lists:
            if node: 
                heap.append((node.val, node))
        heapq.heapify(heap)
        head = ListNode(0); temp = head
        while heap:
            pop = heapq.heappop(heap)
            temp.next = ListNode(pop[0])
            temp = temp.next
            if pop[1].next:
                heapq.heappush(heap,(pop[1].next.val,pop[1].next))
        return head.next