B. So You Think You Can Count?

#include<bits/stdc++.h>
using namespace std;
#define nl "\n"
#define cnl cout << nl;
#define fi first
#define se second
#define pb push_back
#define ll long long
#define ull unsigned ll
#define RV return void
#define sz(x) int(x.size())
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define fixed(n) fixed << setprecision(n)
#define cin(v) for(auto&x:v) cin >> i;
#define cout(v) for(auto&x:v) cout << i << " ";
void files(){
    #ifndef ONLINE_JUDGE
       freopen("input.txt", "r", stdin);
       freopen("output.txt", "w", stdout);
    #endif
}


int n ;
string s;
vector < vector < ll > > dp;
bool valid(int st , int end){
    if(end - st +  1 > 10 ) return false;
    int freq[10]{};
    for(int i = st ; i <= end ; i++){
        if(freq[s[i]-'0'] > 0) return false;
        freq[s[i]-'0']++;

    }

    return true;
}


ll mod = 1e9+7;
ll rec(int idx , int cnt){
    if(idx >= n-1 ) {
        if(idx == n -1 and valid(idx -cnt , idx )) return 1;
        else return 0;
    }

    ll & ret = dp[idx][cnt];
    if(~ret)
        return ret ;
    ret =0;
    if(cnt < 10 ){
        ret +=  rec(idx+1 , cnt+1);
        ret %= mod;
    }

    if(valid(idx-cnt , idx)) {
        ret += rec(idx+1 , 0);
         ret %= mod;
    }

    return ret ;
}
void solve(){


    cin >> n >> s;
    dp.assign(n+1 , vector < ll > (20 , -1));
    cout << rec(0,0) << nl;




}


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

    //  files();
    int testCase=1;
        // cin >> testCase ;
    for(int i=1 ; i <= testCase ; i++){
        solve();
    }

    return 0;
}