solved "Gas Station" on LeetCode http://oj.leetcode.com/problems/gas-station/

gasStation.java

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        size = gas.length;
        if (size == 0) return -1;
        int src = 0, dest = 0, balance = 0;
        while (true) {
            if (balance + gas[dest] - cost[dest] >= 0) {
                balance += gas[dest] - cost[dest];
                dest = next(dest);
                if (dest == src) return src;
            }
            else {
                if (next(dest) <= src) break;
                src = next(dest);
                dest = src;
                balance = 0;
            }
        }
        return -1;
    }

    private int next(int i) {
        return (i+1) % size;
    }

    private int size;
}