Ositus

#include <iostream>
#include <string>
#include <math.h>
using namespace std;

long all(long len) {
    return pow(2, max(len - 1, (long) 0));
}

long solve(string value) {
    long res = 1;

    for (int i = 1; (unsigned) i < value.length(); i++) {
        bool isDup = false;
        long pos = -1;
        for (int j = i; j >= 0; j--) {
            if (value[i] == value[j] && i != j) {
                isDup = true;
                pos = j;
                break;
            }
        }

        if (isDup) {
            res += all(pos + 1) * (all(i - pos) - 1);//+ (pos == 0 ? 0 : 1);
            //cout << value[i] << " i: " << i << " res: " << res << ", pos: " << pos << ", all(pos): " << all(pos + 1) << ", all(i - pos): " << all(i - pos)-1 << "\n";
        } else {
            res *= 2;
            //cout << value[i] << ": " << res << "\n";
        }
    }
    return res;
}

int main() {
    string str;
    cin >> str;
    cout << (solve(str) % 1000000007);

    return 0;
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 4

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 5

Group: 2, 3

Verdict: WRONG ANSWER

Test 6

Group: 3

Verdict: WRONG ANSWER

Test 7

Group: 3

Verdict: WRONG ANSWER