Leetcode-gas station

Title Description:


There was N gas stations along a circular route, where the amount of gas at station I was gas[i].


You had a car with an unlimited gas tank and it costs cost[i] of the gas-to-travel from station I to its next station (I+1). You begin the journey with a 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.


That is, there are N gas stations, to reach the first station of the consumption of cost[i], can find a starting point, you may run GAS[0...N) a circle.








Solution One:


Test each gas station as a starting point (Stopno), respectively, Stopno∈gas[i,n):
Delta= Gasincar (initialized to 0) + gas[i]-cost[i]
If Delta >= 0, accumulate Gasincar, go to the next station I, accumulate the number of successful arrival to the next station: counter. If the counter reaches gas. Length, return I.
Otherwise, reset Gasincar = 0,stopno++. I= Next stop, counter reset to 0.


Due to the time complexity of the solution O (n^2), the test data cannot be passed:


Code:

public int cancompletecircuit (int[] gas, int[] cost) {                var gasincar = 0;        var stopno = 0;                var i = 0;        var counter = 0;        while (Stopno < gas. Length) {                        if (Gas[i] + Gasincar < Cost[i]) {                //failed, start at a new place and re count again                gasincar = 0;                Stopno + +;                i = nextstop (Stopno, gas. Length);                Counter = 0;            }            else{                Gasincar + = Gas[i]-cost[i];                i = nextstop (i, gas). Length);        Counter + +;            }                        if (counter = = gas. Length) {                return i;            }        }                return-1;    }        private int nextstop (int stop,int len) {        if (Stop < len-1) {            stop + +;        }        else {            stop = 0;        }        return stop;    }

Solution Two:
Decompose the problem into two minor problems:
1. Is it possible to complete a lap
2. Find your starting point


The remaining gas in the parking is gasincar=0,delta as the starting point for the gas[i]-cost[i],startat of the current station to the next station.
One traversal gas[i...n-1]:
If delta >= 0:gasincar + = Delta (accumulate gas in the car)
If it is less than 0 (i.e. unreachable): Gasincar is set to Delta,startat = I, that is, resetting the current point as the starting point and gas in the car
Accumulate Totaldelta each time


Finally determine if Totaldelta is greater than 0 = can complete a lap.




Implementation code:

public int cancompletecircuit (int[] gas, int[] cost)     {        var gasincar = 0;     var totaldelta = 0;     var startAt = 0;          for (var i = 0; i < gas. Length; i++) {    var delta = gas[i]-cost[i];         if (gasincar >= 0) {     Gasincar + = Delta;    } else {    gasincar = Delta;    StartAt = i;    }    Totaldelta + = Delta;    }         if (Totaldelta >= 0) {    return startAt;    } else{    return-1;    }    }

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Leetcode-gas station