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.

Analysis: The problem is very similar to the maximum sum in an array.

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        if (gas == null || cost == null || gas.length == 0 || cost.length == 0 || gas.length != cost.length) return -1;
        int startIndex = 0;
        int remainingGas = gas[0] - cost[0]; // temp remaining gas
        int total = gas[0] - cost[0]; // all remaining gas
        for (int i = 1; i < gas.length; i++) {
            if (remainingGas < 0 || remainingGas + gas[i] - cost[i] < 0) {
                startIndex = i;
                remainingGas = gas[i] - cost[i];
            } else {
                remainingGas += (gas[i] - cost[i]);
            }
            total += (gas[i] - cost[i]);
        }
        if (total >= 0 && gas[startIndex] - cost[startIndex] >=0) return startIndex;
        return -1;
    }
}

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