leetcode134. 加油站

class Solution {
    
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
    
       int sum=0;
       for(int i=0;i<gas.size();i++){
    
           sum+=gas[i]-cost[i];
           
       }
       if(sum<0) return -1;
       int start=0,cur=0;
       for(int i=0;i<gas.size();i++){
    
           cur+=gas[i]-cost[i];
           if(cur<0){
    
               cur=0;
               start=i+1;
           }
       }
       return start;
    }
};