Day 13 of Studying LeetCode Solution until I Can Solve One on My Own: Problem134. Gas Station(Medium/JavaScript)

Input: gas = [1,2,3,4,5], cost = [3,4,5,1,2]Output: 3Explanation:Start at station 3 (index 3) and fill up with 4 unit of gas. Yourtank = 0 + 4 = 4Travel to station 4. Your tank = 4 - 1 + 5 = 8Travel to station 0. Your tank = 8 - 2 + 1 = 7Travel to station 1. Your tank = 7 - 3 + 2 = 6Travel to station 2. Your tank = 6 - 4 + 3 = 5Travel to station 3. The cost is 5. Your gas is just enough totravel back to station 3.Therefore, return 3 as the starting index.

Input: gas = [2,3,4], cost = [3,4,3]Output: -1Explanation:You can't start at station 0 or 1, as there is not enough gas totravel to the next station.Let's start at station 2 and fill up with 4 unit of gas. Your tank= 0 + 4 = 4Travel to station 0. Your tank = 4 - 3 + 2 = 3Travel to station 1. Your tank = 3 - 3 + 3 = 3You cannot travel back to station 2, as it requires 4 unit of gasbut you only have 3.Therefore, you can't travel around the circuit once no matterwhere you start.

var canCompleteCircuit = function(gas, cost) {    let start = 0, tank = 0, total = 0//set up a start variable to store the starting gas station's//index if you can travel around the circuit once in the clockwise//direction//set up a tank variable to store remaing gas everytime we get to//a new station, if tank is already less than 0. We will move on//to the next starting index.//set up a total variable, when it is positive, it means there is//enough gas to over all the previous path.    for (let i = 0; i < gas.length; i++){//Loop (note 1) through each station to find the working starting//station        const usage = gas[i] - cost[i]//calculation usage by subtracting the cost to get to the next//station from added gas.        tank += usage//Update tank with usage data (note 4)        if(tank < 0){            tank = 0            start = i + 1        }//if (note 5) tank is less than 0, means the starting station does//not work. We will move on to the next starting station and reset//the tank to 0.        total += usage    }    return total < 0 ? -1 : start//if total is less than 0 (note 3), that means there is not enough//gas to get through all the station.But if it's more than 0,//return the stating point that works.};