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>