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.

Have you been asked this question in an interview?

自己写的代码要冗余一些，下面的是答案。

需要注意的是 index ＋ 1 才表示的是满足条件的station， index 表示的是满足条件的station前面的那个。

index 开始 等于 －1，因为从第0个station 就满足的话，for 循环里 index 不会被付值。

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int num = gas.length;
        int[] remain = new int[num];
        for (int i = 0; i < num; i++) {
            remain[i] = gas[i] - cost[i];
        }
        
        int sum = 0;
        int total = 0;
        int index = -1;

        for(int i = 0; i < gas.length; i++) {
            sum += gas[i] - cost[i];
            total += gas[i] - cost[i];
            if(sum < 0) {
                index = i;
                sum = 0;
            }
        }
        return total < 0 ? -1 : index + 1;
    }
}