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.

读懂题意就好

后面的验证没必要

class Solution {
public:
    int canCompleteCircuit(vector<int> &gas, vector<int> &cost) {
        
        if(gas.size()!= cost.size())return -1;
        int size = gas.size();
        if(size == 0)
        return -1;
        vector<int> left(size,0);
        
        int sum = 0 ; 
        int min = 0 ;
        int min_sum =sum;
        for(int i = 0 ; i < size ;i++)
        {
            left[i] = gas[i] - cost[i];
            sum += left[i];
            if(sum < min_sum){
                min = i;
                min_sum = sum;
            }
        }
        if(sum < 0)return -1;
        sum = 0;
        int index = (min+1)%size;
        for(int  i = 0 ; i < size ;i++)
        {
            sum += left[index];
            index = (index+1)%size;
            if(sum<0)return -1;
        }
        return (min+1)%size;
    }
};