LeetCode-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.
Solution:
Code:

<span style="font-size:14px;">class Solution {
public:
int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
const int length = gas.size();
if (length == 0) return -1;
int totalGas = 0;
int leftGas = 0;
int start = 0;
for (int i = 0; i < length; ++i) {
totalGas += gas[i]-cost[i];
leftGas += gas[i]-cost[i];
if (leftGas < 0) {
start = i+1;
leftGas = 0;
}
}
if (totalGas < 0) return -1;
return start;
}
};</span>