Solution Video: https://www.youtube.com/watch?v=6bvnZzwiKzs

merge_k_sorted_lists.py

import heapq as heap

class HQNode:
    def __init__(self, list_index, val_index, val):
        self.list_index = list_index
        self.val_index = val_index
        self.val = val

    def __eq__(self, other):
        return self.val == other.val
    
    def __gt__(self, other):
        return self.val > other.val
    
    def __ge__(self, other):
        return self.val >= other.val
    
    def __lt__(self, other):
        return self.val < other.val
    
    def __le__(self, other):
        return self.val <= other.val
    
def merge_k_sorted_lists(sorted_lists):
    '''Returns the merged, sorted results of the input list in O(kn log k) time'''
    
    hq = []
    for i, sorted_list in enumerate(sorted_lists):
        heap.heappush(hq, HQNode(i, 0, sorted_list[0]))
    
    results = []
    
    while len(hq) != 0:
        hq_node = heap.heappop(hq)
        
        results.append(hq_node.val)
        
        if hq_node.val_index + 1 < len(sorted_lists[hq_node.list_index]):
            heap.heappush(
                hq,
                HQNode(hq_node.list_index,
                       hq_node.val_index + 1,
                       sorted_lists[hq_node.list_index][hq_node.val_index + 1])
            )
    
    return results

print(merge_k_sorted_lists([[1, 2, 3, 20], [5, 6, 7, 14, 18], [4, 9, 10, 13, 15]]))