Shortest Range in K sorted lists

Given k lists of sorted integers. Find shortest range that includes one number from each of the k lists.
Input:-
L1 :- { 4, 10, 15, 24, 26}
L2 :- { 0, 9, 12, 20 }
L3 :- { 5, 18, 22, 30 }
Output:- {20,24}
Code:-
github.com/IDe...