[LeetCode] Gas Station_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.

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        if (gas == null || gas.length < 1 || cost == null || cost.length != gas.length) {
            return -1;
        }
        
        int len = gas.length;
        int costTotal = 0;
        int gasTotal = 0;
        for (int i = 0; i < len; i++) {
            if (gas[i] >= cost[i]) {
                costTotal = 0;
                gasTotal = 0;
                for (int j = 0; j < len; j++) {
                    int index = (j + i) % len;
                    costTotal += cost[index];
                    gasTotal += gas[index];
                    if (gasTotal < costTotal) {
                        break;
                    }
                }
                
                if (costTotal <= gasTotal) {
                    return i;
                }
            }
        }
        
        return -1;
    }
}