Problem

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.

JavaScript Code

function canCompleteCircuit(gas, cost) {
    var sumRemaining = 0; // track current remaining
    var total = 0; // track total remaining
    var start = 0; 
 
    for (var i = 0; i < gas.length; i++) {
        var remaining = gas[i] - cost[i];
 
        //if sum remaining of (i-1) >= 0, continue 
        if (sumRemaining >= 0) { 
            sumRemaining += remaining;
        //otherwise, reset start index to be current
        } else {
            sumRemaining = remaining;
            start = i;
        }
        total += remaining;
    }
 
    if (total >= 0){
        return start;
    }else{
        return -1;
    }
}
console.log(canCompleteCircuit([1,2,3,4,5],[1,3,2,4,5]));

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