加油站绕圈-单次循环

total合计小于0，必然不能循环

当某个节点的sum小于0时，说明以m开始循环会出现油不够的情况，则进行下一次循环。

    public static void main(String[] args) {
        int[] gas = {2, 3, 1};
        int[] cost = {3, 1, 2};
        System.out.println(canCompleteCircuit3(gas, cost));
    }

    /**
     * @param gas=[2,3,1]
     * @param cost=[3,1,2]
     * @returnss
     */
    public static int canCompleteCircuit3(int[] gas, int[] cost) {
        int sum = 0;
        int total = 0;
        int start = 0;
        for (int m = 0; m < gas.length; m++) {
            total += gas[m] - cost[m];
            sum += gas[m] - cost[m];
            if (sum < 0) {
                start=m+1;
                sum = 0;
            }
        }
        return total < 0 ? -1 : start;
    }

算法参考：https://www.cnblogs.com/grandyang/p/4266812.html

https://www.cnblogs.com/MrSaver/p/9644679.html