Given max. travel distance and forward and backward route list, return pair of ids of forward and backward routes that optimally utilized the max travel distance.:

eg: max travel distance is : 11000
forward route list : [[1,3000],[2,5000],[3,4000],[4,10000]]
backward route list : [[1,2000],[2,3000],[3,4000]]

Result : [2,3] ...2 is from forward and 3 is from backward...total distance is 9000...no other combination is there which is >9000 and <=11,000