Merge K Sorted Lists with Key-Value Pairs

Given k linked lists, each containing (key, value) pairs, return a merged list that is sorted by keys. If the key appears in more than one list, the latest occurrence in the lists should overwrite the previous ones. Input: k = 3 l0 = [(1,70),(3,20),(5,30)] l1 = [(2,40),(3,50)] l2 = [(1,15),(4,80),(5,90)] Output: answer = [(1,15),(2,40),(3,50),(4,80),(5,90)] Example Input 3 [(1,70),(3,20),(5,30)] [(2,40),(3,50)] [(1,15),(4,80),(5,90)]