Ositus

import java.util.Arrays;
import java.util.Scanner;

public class Merkkijono {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String s = scanner.next();
        char[] ar = s.toCharArray();
        long total = 1;
        int last = -1;
        int[] chars = new int[123];
        Arrays.fill(chars, -1);
        chars[s.charAt(0)] = 0;
        int mins = 0;
        for (int j = 1; j < ar.length; j++) {
            char c = ar[j];

            int i;
            total *= 2;
            int min=0;
            if ((i = chars[c]) != -1) {
                if (i > last) {
                    last = i;
                    int m = (int) (Math.pow(2,i));
                    min =  m - mins;
                    total -= min;
                }
            }
            mins *= 2;
            mins += min;

            total = total % 1_000_000_007;
            chars[c] = j;
        }
        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: ACCEPTED

Test 5

Group: 2, 3

Verdict: WRONG ANSWER

Test 6

Group: 3

Verdict: WRONG ANSWER

Test 7

Group: 3

Verdict: WRONG ANSWER