leetcode---gas-station---贪心

There are N gas stations along a circular route, where the amount of gas at station i isgas[i].
You have a car with an unlimited gas tank and it costscost[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.

class Solution {public:    int canCompleteCircuit(vector<int> &gas, vector<int> &cost)     {        int n = gas.size();        if(n == 0)            return 0;        int gasSum = 0, costSum = 0;        for(int i=0; i<n; i++)        {            gasSum += gas[i];            costSum += cost[i];        }        if(gasSum < costSum)            return -1;        int maxDis = -1, id = 0;        for(int i=0; i<n; i++)        {            int tmp = 0;            tmp += gas[i] - cost[i];            if(tmp < 0)                continue;            for(int j=i+1; j!=i; (++j)%=n)            {                tmp += gas[j%n] - cost[j%n];                if(tmp < 0)                    break;            }            if(tmp > maxDis)            {                maxDis = tmp;                id = i;            }        }        return id;    }};