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 costscost[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.

 

Given 4 gas stations with gas[i]=[1,1,3,1], and thecost[i]=[2,2,1,1]. The starting gas station's index is 2.

 

public class Solution {    /**     * @param gas: an array of integers     * @param cost: an array of integers     * @return: an integer     */    public int canCompleteCircuit(int[] gas, int[] cost) {        // write your code here                if(gas == null || gas.length == 0 || cost == null || cost.length == 0 || gas.length != cost.length)            return -1;                int gas_sum = 0;        int cost_sum = 0;                for(int i = 0; i < gas.length; i++)            gas_sum += gas[i];                for(int i = 0; i < cost.length; i++)            cost_sum += cost[i];                if(gas_sum < cost_sum)            return -1;                int left = 0;        int start = 0;                while(start < gas.length){            int i = start;                        for(; i < gas.length; i++){                left += gas[i];                left -= cost[i];                                if(left < 0){                    left = 0;                    break;                }            }                        if(i != gas.length)                start = i + 1;            else                return start;        }                return -1;    }}