Who crosses Time Side A Side B ----------- ---- ------ ------ (Start) 1,2,3,4 1,2 A->B 2 3,4 1,2 1 B->A 1 1,3,4 2 3,4 A->B 10 1 2,3,4 2 B->A 2 1,2 3,4 1,2 A->B 2 -- 1,2,3,4Total time 17 minutes.
The problem with finding the solution is that people usually use a heuristic that makes sense, specifically that you want someone fast to walk with someone slow so that you have someone fast to walk the flashlight back. This ignores the overhead that you are wasting, if you do something like walk man 1 with man 4, where you have 9 minutes of overhead, some of which could be used to cross man 3 (as in the solution above.