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.

class Solution {
public:
int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
int start = gas.size();
if(start<=0) return -1;
int cur=0;
int left = 0;
while(cur!=start){
if( gas[cur] +left >= cost[cur]){
left+= gas[cur]- cost[cur];
++cur;
}else{
--start;
left+= gas[start]- cost[start];
}
}
if(left < 0) return -1;
return start%gas.size();
}
};