Algorithm for truck moving around a circle of gas stations

Question

You have a truck moving around a circular track with gas stations spaced out around the circle. Each station has a finite amount of gas. The gas tank on the truck is infinit

Answer 1

starting from any station, try to move to the next one (to the right). If you can't (run out of gas), we have to take gas from the left of the starting point (move starting station to the left).

    start = 0
    end = start
    amount = 0
    for i in range(n):
        if amount > 0:
            amount += (gas[end] - cost[end])
            end = (end + 1) % n
        else:
            start = (start - 1 + n) % n
            amount += (gas[start] - cost[start])

    if amount >= 0: return start    
    return -1

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