[leetcode]Gas Station

问题描述：

There are N gas stations along a circular route, where the amount of gas at stationi is gas[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.

Note:
The solution is guaranteed to be unique.

代码：

int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {  //C++        if(gas.size()==0|| cost.size()==0||gas.size()!=cost.size())            return -1;                    int size = gas.size();        vector<int> left(size);        for(int i=0; i<size; i++)            left[i]=gas[i]-cost[i];                int max=left[0],begin=0,temp=0,index=begin;        for(int i=0; i<size; i++ ){            temp += left[i];            if(temp > max){                max = temp;                index = begin;            }            if(temp < 0){                temp = 0;                begin = i+1;            }        }        if(temp >=0 && begin !=0){            for(int i=0; i<size; i++){                temp += left[i];                if(temp > max){                    max =temp;                    index = begin;                }                if(temp <0)                    break;            }        }        temp = 0;        for(int i=0; i<size; i++ )        {            temp +=left[(i+index)%size];            if(temp <0)                return -1;        }        return index;    }