Gas Station

There are N gas stations along a circular route, where the amount of gas at station i is gas[i].
You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1).
You begin the journey with an empty tank at one of the gas stations.
Return the starting gas station's index if you can travel around the circuit once, otherwise return -1.

Note: The solution is guaranteed to be unique.

1. If the sum of gas[i] is less than the sum of cost[i], for sure we should return -1. However, is it possible that we cannot travel around the circuit from any starting gas stations, even if the sum of gas[i] is greater than the sum of cost[i]? The answer is no since we have unlimited gas tank.

2. If we cannot travel from station i to station j, is it possible that the available starting point is located between i and j?

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