Leetcode152: 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) {        if(gas.size()==0 || cost.size()==0 || gas.size()!=cost.size())  return -1;        int sum = 0;        int total = 0;        int start = 0;        for(int i = 0; i < gas.size(); i++)        {            total += gas[i]-cost[i];            if(sum<0)            {                sum = gas[i]-cost[i];                start = i;            }            else                sum += gas[i]-cost[i];        }        return total<0? -1:start;    }};