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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.

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class Solution {

public:

int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {

int total = 0;

int sumRemaining = 0;

int remain = 0;

int start;

for(int i=0;i<gas.size();i++)

{

remain = gas[i]-cost[i];//how much remaining for each gas station

if(sumRemaining>=0) // if accumulated gas is less than, it should be reset.

{

sumRemaining = sumRemaining+remain;

}

else //reset.

{

sumRemaining = remain;

start = i;

}

total+=remain;

}

if(total>=0) return start;

else return -1;

}

};