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.

思路： 从第一个点开始，查看可以允许的长度，如果和为负数，则重新开始计数；并且要记录总路径之和，只有总路径之和大于等于0，才能够保证可以转一圈。

JAVA 代码：

1. public int canCompleteCircuit(int[] gas, int[] cost) {
2. int start = 0;
3. int sum = 0; // judge the current start is ok
4. int total = 0; // ensure the circle is ok
5. for(int i = 0 ;i<gas.length;i++) {
6. sum += gas[i] - cost[i];
7. total += gas[i] - cost[i];
8. if(sum < 0) {
9. start = i+1;
10. sum = 0;
11. }
12. }
13. if(total<0) return -1;
14. return start;
15. }