Ositus

#include <bits/stdc++.h>

using namespace std;

#define M 1000000007

typedef long long int ll;

string s;
ll r,vr;
map<char,pair<ll,ll>> m;

int main()
{
    cin>>s;
    for(char c : s)
    {
        if(r == 0)
        {
            r++;
        }
        else
        {
            r *= 2;
            ll cvr = vr - m[c].second;
            cvr = cvr > 0 ? cvr : 0;
            cvr = m[c].first - cvr;
            cvr = cvr > 0 ? cvr : 0;
            r -= cvr;
            vr += cvr;
        }
        r %= M;
        vr %= M;
        m[c] = make_pair(r,vr);
    }
    if(r<0) r += M;
    cout<<r;
}

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: WRONG ANSWER

Test 6

Group: 3

Verdict: WRONG ANSWER

Test 7

Group: 3

Verdict: WRONG ANSWER