Project Euler #32 : Pandigital products

llong solve(VLL p, int index1, int index2) {
    int pow = 1, prod1 = 0, prod2 = 0, prod3 = 0;
    for (int i = index1; i >= 0; i--) {
        prod1 += pow * p[i];
        pow *= 10;
    }
    pow = 1;
    for (int i = index2; i > index1 ; i--) {
        prod2 += pow * p[i];
        pow *= 10;
    }
    pow = 1;
    for (int i = 8; i > index2; i--) {
        prod3 += pow * p[i];
        pow *= 10;
    }
    return (prod1 * prod2 == prod3) ? prod3 : 0;
}
 
int main() {
    llong sum = 0;
    set<llong> a;
    VLL p = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    do {
        for (int i = 0; i < 8; i++) {
            for (int j = i + 1; j < 8; j++) {
                int x = solve(p, i, j);
                if (x != 0 && a.count(x) == 0) {
                    sum += x;
                    a.insert(x);
                }
            }
        }
    } while (next_permutation(p.begin(), p.end()));
    cout << sum;
}