Leetcode: 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.

 1 public class Solution {
 2     public int canCompleteCircuit(int[] gas, int[] cost) {
 3         int N = gas.length;
 4         int[] balance = new int[N];
 5         for (int i = 0; i < N; i++) {
 6             balance[i] = gas[i] - cost[i];
 7         }
 8         
 9         for (int k = 0; k < N; k++) {
10             if (check(balance, k, N) == 1) return k;
11         }
12         return -1;
13     }
14     
15     public int check(int[] balance, int k, int N) {
16         int sum = 0;
17         for (int j = 0; j < N; j++) {
18             if (k + j < N) sum = sum + balance[k+j];
19             else sum = sum + balance[k+j-N];
20             if (sum < 0) return 0;
21         }
22         return 1;
23     }
24 }