gas-station

There are N gas stations along a circular route, where the amount of gas at station i isgas[i].

You have a car with an unlimited gas tank and it costscost[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.

//题目求解，求解最大diff=gas[i]-cost[i]的最大值。贪心算法，如果sum<0 从该节点重新开始计算。

class Solution {
public:
    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
        if(gas.size()==0 || cost.size()==0 || gas.size()!=cost.size()) return 0;
        
        int total = 0,sum = 0,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;
    }
};