Gas Station

There are N gas stations along a circular route, where the amount of gas at stationi is gas[i].

You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from stationi 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.

Solution:

class Solution {public:    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {        int total = 0, sum = 0, index = 0;        for(int i = 0; i < gas.size(); ++i)        {            sum += gas[i] - cost[i];            total += gas[i] - cost[i];            if(sum < 0)            {                index = i + 1;                sum = 0;            }        }                return total < 0 ? -1 : index;    }};