Details of the problem ...

Input is crossing time list. (for example x= [1 2 5 8])

Output is the length of all possible crossing time records. (for original problem y_correct= 14. In other words it is possible to cross the bridge in [15, 17, 18, 19, 21, 22, 24, 25, 27, 28, 30, 31, 34, 40] minutes.

Assumption 1: for this problem only four people will cross the bridge

Assumption 2: crossing times are integer

Crossing Model: 2 out of 4 people will cross the bridge, one of them will return. two out of 3 people will cross the bridge, one out of three people will return. Remaining two people will cross the bridge.