134. 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.
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解决代码：

class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        if(gas.size()==0||cost.size()==0||gas.size()!=cost.size()) 
        return -1;
        int sum=0,total=0,begin=0;
        for(int i=0;i//用作判断是否中途汽油为负
            total+=(gas[i]-cost[i]);//计算跑完全程所剩汽油
            if(sum<0)
            {
                begin=i+1;//若中途汽油为负,则从下一个加油站开始算
                sum=0;
            }
        }
        return total<0?-1:begin;
    }
};