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.

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

		int index = 0;
		total = 0;
		for (int i = 0; i < size; i++)
		{
			total += left[i];
			if (total < 0)
			{
				index = i + 1;
				total = 0;
			}
		}
		return index;		
	}
};