循环数组

There are N gas stations along a circular route, where the amount of gas at station i isgas[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.

Note: 
The solution is guaranteed to be unique

 

class Solution {
public:
int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
　　int n=gas.size();

　　for(int i=0;i<n;i++)
　　{
　　int sum=gas[i]-cost[i];
　　int j=(i+1)%n;//注意这增加的时候取余数

　　for(;sum>=0;j=(j+1)%n)
　　{
　　sum+=gas[j]-cost[j];
　　if(j==i)
　　break;
　　}
　　if(j==i &&sum>=0)
　　return i;

　　}
　　return -1;
}
};