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.

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int dif [] = new int[gas.length];
        for(int i=0;i<gas.length;i++){
            dif[i] = gas[i] - cost[i];
        }
        int left = 0;
        int sum = 0;
        int start =0;
        for(int i=0;i<gas.length;i++){
            left +=dif[i];
            sum += dif[i];
            if(sum<0){
                sum=0;
                start = i+1;
            }
        }
        return left<0?-1:start;
    }
    
}