*leetcode #134 in cpp

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.

Solution:

http://bangbingsyb.blogspot.com/2014/11/leetcode-gas-station.html

Code:

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