Ositus

import java.util.Scanner;

public class Merkkijono {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.next();
        StringBuilder builder = new StringBuilder(s.charAt(0)+"");
        char[] ar = s.substring(1).toCharArray();
        long total = 1;
        for (char c : ar) {
            int i;
            boolean uneven=false;
            if ((i = builder.lastIndexOf(c+"")) != -1) {
                int min = builder.length()-1-i;
                if (min % 2 != 0) {
                    uneven = true;
                }
                total -= min/2;
            }
            total *= 2;
            if (uneven) {
                total-=1;
            }
            total = total % 1_000_000_007;
            builder.append(c);
        }
        System.out.println(total);
    }
}

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