GasStation.java

/**
 * 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 class GasStation {
	public int canCompleteCircuit(int[] gas, int[] cost) {
		int sum = 0, total = 0, len = gas.length, index = -1;
		for (int i = 0; i < len; i++) {
			sum += gas[i] - cost[i];
			total += gas[i] - cost[i];
			if (sum < 0) {
				index = i;
				sum = 0;
			}
		}
		return total >= 0 ? index + 1 : -1;
	}
}