make the full circular path, shortest path exercise?

Question

I got this question in an interview and I was not able to solve it.

You have a circular road, with N number of gas stations. You know the ammount of gas

Answer 1

This is optimized case of @George Duckett's answer.

• Choose and remember your start station.
• Loop(1) through stations clockwise.
  • Get a fuel.
  • If you have enough fuel, go to next station, decrease remaining fuel amount, continue loop(1)

If you reached your start station - problem solved.

If on some station you do not have enough fuel to reach next one

• Remember your end station.
• Distance_to_start = 0, fuel_to_start = 0
• Loop(2) from your start station counterclockwise.
  • Add available fuel and distance to next station to your counters
  • If fuel_to_start > distance_to_start, you have some excess fuel. Mark this station as your new start and go to loop(1) again - may be you can go ahead now.
  • Otherwise, continue loop(2)

If you had gone counterclockwise to already visited station - bad luck, there is not enough fuel on stations to go full circle.