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.

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

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