Gas Station

int Solution::canCompleteCircuit(const vector<int> &A, const vector<int> &B) {
    vector<int> maxiDiffIndex;
    int n = A.size();
    int maxi = -1e9;

    for(int i=0; i<n; ++i){
        maxi = max(maxi, A[i]-B[i]);
    }

    for(int i=0; i<n; ++i){
        if(A[i]-B[i]==maxi){
            maxiDiffIndex.push_back(i);
        }
    }

    int ans = -1;
    for(auto index: maxiDiffIndex){
        int a = index;
        int sum = 0;
        bool flag = true;

        for(int j=0; j<n; ++j){
            int i = a+j;
            i%=n;
            sum += A[i]-B[i];
            if(sum<0){
                flag = false;
                break;
            }
        }
        if(flag){
            return a;
        }
    }

    return ans;
}