[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;
    }
};