Gas Station
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.
思路：顺序扫一圈。如果总油量小于总消耗，说明起点错误，则将起点往后移位。
几个地方需要注意：
1、如果有解，则终点绕一圈之后回到起点
2、最多绕一圈即可判断是有解还是无解，起点重复代表无解
3、终点必须在起点之后
class Solution { public: int canCompleteCircuit(vector<int> &gas, vector<int> &cost) { vector<int>::size_type size = gas.size(); int start = 0; int finish = 0; int totalGas = gas[start]; int totalCost = cost[start]; while(finish != start+size) {//if finish == start+size, finish if(totalGas >= totalCost) { finish ++; totalGas += gas[finish%size]; totalCost += cost[finish%size]; } else { totalGas -= gas[start]; totalCost -= cost[start]; start ++; if(start == size) return -1; //no solution //restart here if(finish+1 == start) { finish ++; totalGas = gas[start]; totalCost = cost[start]; } } } return start; } };
原文：http://www.cnblogs.com/ganganloveu/p/4117531.html