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.

Java

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int start = 0, netGasSum = 0, curGasSum = 0;

        for(int i = 0; i < gas.length; i++) {
            netGasSum += gas[i] - cost[i];
            curGasSum += gas[i] - cost[i];

            if(curGasSum < 0) {
                start = i + 1;
                curGasSum = 0;
            }
        }

        return netGasSum < 0 ? -1 : start;
    }
}