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.

• Time: O(n)
• Space: O(n)

public int canCompleteCircuit(int[] gas, int[] cost) {
    int sum = 0, total = 0, ret = -1;
    for (int i = 0; i < gas.length; i++) {
        sum += gas[i] - cost[i];
        total += gas[i] - cost[i];
        if (sum < 0) {
            ret = i;
            sum = 0;
        }
    }
    return total >= 0 ? ret + 1 : -1;
}