unsigned long hackerrankCity(vector<int> A) {
    int mod = 1000000007;
    unsigned long P = 1, L = 0, D = 0, H = 0;
    for (int i=1; i <= A.size(); i++) {
        H = (4*H + 12*P*D + 16*((P*P) % mod)*A[i-1] + 8*D + 12*P*A[i-1] + A[i-1]) % mod;
        D = (3*P*L + 8*P*A[i-1] + 4*D + 2*L + 3*A[i-1]) % mod;
        P = (4*P + 2) % mod;
        L = (2*L + 3*A[i-1]) % mod;
    }
    return H;
}