Ositus

#include <bits/stdc++.h>

using namespace std;

#define ull unsigned long long
#define ll long long
ull ans = 0;

vector<ull> cache;
string line;

ull calc(ull startOffset){
    ull fnd[28] = {0};
    bool brk = false;
    ull tmpAns = 0ull;
    for (ull i = startOffset; i < line.length(); ++i) {
        fnd[line[i]-97]++;
        if(fnd[line[i]-97] > 1) {
            brk = true;
            break;
        }
        if(i == line.length()) {
            break;
        }
        if(cache[i+1] == -1ull){
            tmpAns = (tmpAns + calc(i+1)) % (1000000007ull);
        }else{
            tmpAns = (tmpAns + cache[i+1]) % (1000000007ull);
        }
    }
    if(!brk){
        tmpAns = (tmpAns + 1) % (1000000007ull);
    }
    cache[startOffset] = tmpAns;
    return tmpAns;
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);


    std::getline(std::cin, line);

    cache = vector<ull>(line.length() + 1, -1);

    for (int i = line.length()-1; i >= 0; --i) {
        calc(i);
    }

    ans += calc(0);

    cout << (ans/2) % (1000000007ull);
    cout << '\n';
    flush(std::cout);
}

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