[LeetCode] Gas Station

int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
	vector<int> gasLeft;
	for(int i = 0; i < gas.size(); i++) {
		gasLeft.push_back(gas[i] - cost[i]);
	}
	int startStation = 0, gasBalance = 0, gasCost = 0;
	for(int i = 0; i < gasLeft.size(); i++) {
		gasBalance += gasLeft[i];        
		if(gasBalance < 0) {
			gasCost = gasBalance;
			startStation = i+1;
			gasBalance = 0;
		}        
	}
	if((gasBalance+gasCost) < 0) {
		return -1;
	}
	else {
		return startStation;
	}
}