Ositus

#include <iostream>
#include <string>
#include <set>
#define mod 1000000007
#define ll long long

using namespace std;

ll int dp[1000100];
string str;

ll int find_ans(unsigned ll int ind){
    set<char> chars;
    ll int first_ind = ind;
    ll int ans = 0;
    if(ind == str.length() - 2){
        if(str[ind] == str[ind+1]){dp[ind] = 1; return 1;}
        else{dp[ind] = 2; return 2;}
    }
    if(ind > str.length() - 2)return 1;
    while(true){
        if(ind > str.length()-1 || chars.find(str[ind]) != chars.end())break;
        chars.insert(str[ind]);
        ++ind;
        if(ind > str.length()-1)ans += 1;
        else{
        if(dp[ind] == -1){
        ans = (ans + find_ans(ind)) %mod;}
        else{ans = (ans + dp[ind])%mod;}
    }}
    dp[first_ind] = ans %mod;
    ans = ans %mod;
    return ans;
}

int main()
{
    for(int i = 0; i < 1000100; ++i){
    dp[i] = -1;
}

    string x; getline(cin, x);
    if(x.length() == 1)cout << 1;
    else{
    dp[x.length()-1] = 1;
    str = x;
    cout << find_ans(0);}








    return 0;
}

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: ACCEPTED