Gas Station

Write `can_complete_circuit(gas, cost)` returning the starting index from which you can drive the whole circle, or `-1`. You start with an empty tank. gas = [1,2,3,4,5], cost = [3,4,5,1,2] -> 3 If the total gas is at least the total cost, a solution exists and it is unique. One pass: whenever the running tank goes negative, no station from the old start through here can work, so restart at the next one. Be ready to prove that — it is the entire question.