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.

一刷
题解：
如果A不能到达B，那么AB间的所有station都不能到达B
如果总的cost>gas, 那么从所有的stop都不能完成一次循环

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int start = 0, total = 0, tank = 0;
        for(int i=0; i<gas.length; i++){
            tank += gas[i] - cost[i];
            if(tank<0){
                start = i+1;
                total += tank;
                tank = 0;
            }
        }
        return total+tank<0? -1:start;
    }
}

二刷
思路同1刷

public class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        int start = 0, total = 0, tank = 0;
        for(int i=0; i<gas.length; i++){
            tank+= gas[i] - cost[i];
            if(tank<0){
                start = i+1;
                total+= tank;
                tank = 0;
            }
        }
        if(total+tank>=0) return start;
        else return -1;
    }
}