原题链接: https://oj.leetcode.com/problems/gas-station/

public int canCompleteCircuit(int[] gas, int[] cost) {
    if (gas == null || cost == null || gas.length != cost.length) {
        return -1;
    }

    int totalGas = 0;
    int subSeqGas = 0;
    int start = 0;
    for (int i = 0, numGasStation = gas.length; i < numGasStation; i++) {
        subSeqGas += gas[i] - cost[i];
        totalGas += gas[i] - cost[i];

        if (subSeqGas < 0) {
            subSeqGas = 0;
            start = i + 1;
        }
    }

    return totalGas >= 0 ? start : -1;
}

public int canCompleteCircuit(int[] gas, int[] cost) {
    // brute force (will meet time limit exceed)

    if (gas == null || cost == null || gas.length != cost.length) return -1;

    int numGasStation = gas.length;
    int remainGas = 0;
    int start = 0;
    boolean found = false;

    while (!found && start < numGasStation) {
        remainGas = 0;

        for (int index = start;;) {
            remainGas += gas[index];

            if (remainGas >= cost[index]) {
                remainGas -= cost[index];

                if (index == numGasStation - 1) {
                    index = 0;
                } else {
                    index++;
                }

                if (index == start) {
                    found = true;
                    break;
                }
            } else {
                start++;
                break;
            }
        }

    }

    return found ? start : -1;
}