Ositus

//package me.anttono;

import java.math.BigInteger;
import java.util.AbstractMap;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {

    public static final int M = 1000000007;

    public static void main(String[] args)
    {
        BigInteger r = BigInteger.ZERO;
        BigInteger vr = BigInteger.ZERO;
        Map<Character, AbstractMap.SimpleEntry<BigInteger, BigInteger>> m = new HashMap<>();

        Scanner scanner = new Scanner(System.in);
        String s = scanner.nextLine();

        for(char c : s.toCharArray())
        {
            if(m.get(c)==null) m.put(c, new AbstractMap.SimpleEntry<>(BigInteger.ZERO, BigInteger.ZERO));
            if(r.equals(BigInteger.ZERO)) r = BigInteger.ONE;
            else
            {
                r = r.multiply(BigInteger.valueOf(2));
                BigInteger cvr = m.get(c).getKey().subtract(vr.subtract(m.get(c).getValue()));
                cvr = cvr.compareTo(BigInteger.ZERO) >= 0 ? cvr : BigInteger.ZERO;
                r = r.subtract(cvr);
                vr = vr.add(cvr);
            }
            m.put(c, new AbstractMap.SimpleEntry<>(r, vr));
        }

        System.out.println(r.mod(BigInteger.valueOf(M)));
    }
}

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 2, 3

Verdict: ACCEPTED

Test 6

Group: 3

Verdict: ACCEPTED

Test 7

Group: 3

Verdict: TIME LIMIT EXCEEDED