0134. Gas Station

class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int n = gas.length;
        int sumGas = 0, sumCost = 0;
        for (int i = 0; i < n; i++) {
            sumGas += gas[i];
            sumCost += cost[i];
        }
        if (sumCost > sumGas) {
            return -1;
        }
        int sum = 0;
        int res = 0;
        for (int i = 0; i < n; i++) {
            sum += (gas[i] - cost[i]);
            if (sum < 0) {
                sum = 0;
                res = i + 1;
            }
        }
        return res;
    }
}