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.

gas的和必须大于等于cost，如果在i处gas和小于cost，i为起点。

public int canCompleteCircuit(int[] gas, int[] cost) {
	int start=0,total=0,totalDiff=0;
	for(int i=0;i<gas.length;i++){
		int dif=gas[i]-cost[i];
		if(totalDiff>=0)
			totalDiff+=dif;
		else{
			totalDiff=dif;
			start=i;
		}
		total+=dif;
	}
	if(total>=0)
		return start;
	else
		return -1;
}