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

MERGEKLIST.py

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

class Solution:
    # @param A : list of linked list
    # @return the head node in the linked list
    def mergeKLists(self, A):
        if len(A) == 0 :
            return []
        heap = []
        res = ListNode(0)
        temp = res
        for i in range(len(A)) :
            if  A[i] :
                heapq.heappush(heap,( A[i].val, i))
        while heap :
            val, i = heapq.heappop(heap)
            temp.next =  A[i]
            A[i] = A[i].next
            temp = temp.next
            if A[i] :
                heapq.heappush(heap, (A[i].val, i))
        temp.next = None
        return res.next