[LeetCode]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.

思考：若sum<0，则可能从下一站开始。

class Solution {

public:

    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {

        int n=gas.size();

        int sum=0;

        int index=0;

        int total=0;

        for(int i=0;i<n;i++)

        {

            sum+=gas[i]-cost[i];

            total+=gas[i]-cost[i];

            if(sum<0) 

            {

                index=(i+1)%n;

                sum=0;

            }

        }

        if(total<0) return -1;

        else return index;

    }

};