LeetCode OJ——Gas Station

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) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        size_t i,j;
        vector<int> left;
        int sum=0;
        for(i=0;i<gas.size();i++){
            left.push_back(gas[i]-cost[i]);
            sum+=left[i];
        }
        if(sum<0){
            return -1;
        }
        for(i=0;i<gas.size();i++){
            j=i;
            sum=0;
            while(1){
                sum+=left[j];
                j++;
                if(j==gas.size()){
                    j=0;
                }
                if(sum<0){
                    break;
                }
                else{
                    if(j==i){
                        return i;
                    }
                }
            }
        }
    }
};