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.

    public int canCompleteCircuit(int[] gas, int[] cost) {
        int len = gas.length;
    	int i = 0;
        
    	while(i < len) {
    		int curGas = 0;
    		int cur = i;
    		int j = i;
    		boolean flag = false;
    		do{
    			curGas += gas[j % len];
    			curGas -= cost[j % len];
    			if (curGas >= 0) {
    				flag = true;
    			} else {
    				flag = false;
    			}
    			j++;
    		}while(flag && (j % len) != cur);
    		
    		if ((j % len) == i && flag == true) {
    			return i;
    		}
    		i = j;
        }
    	return -1;
    }