LeetCode-gas-station

There are N gas stations along a circular route, where the amount of gas at station i isgas[i].

You have a car with an unlimited gas tank and it costscost[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) {
        int [] rest = new int [gas.length];
         
        int res = 0;
         
        for(int i = 0; i < gas.length; ++i){
            rest[i] = gas[i] - cost[i];
            res += rest[i];
        }
         
        if(res < 0)
            return -1;
        int len = rest.length;
        for(int i = 0; i < rest.length; ++i){
            int start = (i+1)%len;
            int end = i;
            int total = rest[i];
            if(total < 0)
                continue;
            while(start != end){
                total += rest[start];
                if(total < 0)
                    break;
                start = (start + 1)%len;
            }
            if(total >= 0)
                return i;
            else
                continue;
        }
        return -1;
         
    }
}