Puzzle 2➤ Crossing the Bridge riddle
This is a popular question asked during the interviews. So we need some thought process to find out the winning solution.
The thought process to decide upon the optimum strategy:
There are 4 persons (A, B, C, and D) who want to cross a bridge in the night.
- A takes 1 minute to cross the bridge.
- B takes 2 minutes to cross the bridge.
- C takes 5 minutes to cross the bridge.
There is only one torch with them and the bridge cannot be crossed without the torch. There cannot be more than two persons on the bridge at any time.
- D takes 10 minutes to cross the bridge.
What is the shortest time needed for all four of them to cross the bridge?
The Answer To The Puzzle 2➤
This is a popular question asked during the interviews. So we need some thought process to find out the winning solution.
The thought process to decide upon the optimum strategy:
- Always make sure that the 2 persons together cross the bridge towards their camp.
- Ensure that the fastest available person on the camp side to bring the torch to the other side.
- Ensure that none of the two slowest persons among the four of the team (in this case the 5 & the 10) cross the bridge more than once. So they can't be allowed to cross the bridge in the first trip as well as on the last trip.
- So, in the first trip, the two fastest persons in the team (in this case, the 1 and the 2) cross the bridge towards their camp. And, any one of them (ie either 1 or 2) comes back and hands over the torch to 5 and 10.
- Once they arrive at camp, 2 or 1 (as the case may be), brings to rescue 1 or 2 (as the case may be).
So, The final plan➤
- 1 & 2 cross; 1 OR 2 remains; 2 OR 1 returns=> Time taken: 2+2=4' OR 2+1=3'.
- 5 & 10 arrives at camp and remain there. 1 OR 2 returns=> Time taken: 10+1=11 OR 10+2=12'.
- 1 AND 2 arrive at camp=>Time taken=2'
