Ositus

#include <bits/stdc++.h>

using namespace std;

int main() {
    string str; cin >> str;
    vector<int> points(str.length(), 0);
    unordered_set<char> seen;

    auto ita = str.rbegin();
    auto itb = ita+1;

    seen.insert(*ita);

    while (ita != str.rend()) {
        int bi = str.rend()-itb-1;

        if (seen.find(*itb) == seen.end() && itb != str.rend()) {
            seen.insert(*itb);
            points[bi] += 1;
            ++itb;
        } else {
            ++ita;
            itb = ita+1;
            seen.clear();
        }
    }

    for (int i = points.size()-1; i >= 0; --i) {
        points[i] += points[i+1];
    }

    points[points.size()-1] = 1;

    int result = 0;

    auto itc = str.begin();
    auto itd = itc+1;

    seen.clear();
    seen.insert(*itc);

    while (itc != str.end()) {
        int di = distance(str.begin(), itd)-1;

        cout << *itc << " and " << *itd << endl;

        if (seen.find(*itd) == seen.end() && itd != str.end()) {
            cout << "YES! i=" << di+1 << endl;
            seen.insert(*itd);
            result += points[di+1+1]+1;
            ++itd;
        } else {
            cout << "fail." << endl;
            ++itc;
            itd = itc+1;
            seen.clear();
        }
    }

    if (result%2==1)--result;

    cout << result%1000000007 << endl;
}

Test 1

Group: 1, 2, 3

Verdict: WRONG ANSWER

Test 2

Group: 1, 2, 3

Verdict: WRONG ANSWER

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: TIME LIMIT EXCEEDED