gas_station.cpp

#include<bits/stdc++.h>
using namespace std;


class Solution {
public:
    int canCompleteCircuit(vector<int>& gas, vector<int>& cost) {
        int n = gas.size();
        int total_surplus = 0;
        int surplus = 0;
        int start = 0;

        for(int i=0;i<n;i++){
            total_surplus += gas[i] - cost[i];
            surplus += gas[i] - cost[i];
            if(surplus < 0){
                surplus = 0;
                start  = i+1;
            }
        }
        return (total_surplus < 0) ? -1 : start;
    }
};