[leetcode] GasStation

/**
* <pre>
* 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.
* </pre>
* */
public class GasStation {
    public class Solution {
        public int canCompleteCircuit(int[] gas, int[] cost) {
            int n = gas.length;
            int start = 0;
            int left = gas[0] - cost[0];
            int next = (start + 1 + n) % n;
            while (start != next) {
                if (left < 0) {
                    start = (start - 1 + n) % n;
                    left = left + gas[start] - cost[start];
                } else {
                    left = left + gas[next] - cost[next];
                    next = (next + 1 + n) % n;
                }
            }
            if (left >= 0)
                return start;
            else
                return -1;
        }
    }
}