Gas Station

题目原型：

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.

基本思路：

遍历一圈，如果说剩下的油和待加的油能够走过这一站的话则继续，否则改变起点继续，当起点回到原来走过的点时表示不能

public int canCompleteCircuit(int[] gas, int[] cost){if(gas.length==0||gas==null)return -1;if(cost.length==0||cost==null)return 0;int index = 0;int rest = 0;//还剩多少油int count = 0;//走过的长度int startIndex = 0;//起始点int len = gas.length;boolean isCircle = false;//记录是否回到了曾经走过的点while(count<len){if(rest<0||rest+gas[index]<cost[index]){startIndex = (index+1)%len;//起点回到曾经走过的点那么就说明不能通过if(isCircle)return -1;count = 0;}else{rest = rest + gas[index] - cost[index];count++;}if(index+1>=len)isCircle=true;index = (index+1)%len;}return startIndex;}

绕一圈。