Distinct Split

#include <bits/stdc++.h>
using namespace std;

#define ll long long
const int M = 1e9+7;
const int N = 1e7+5;

int main() {
    int t;
    cin >> t;
    while (t--) {
        string s;
        ll n;
        cin >> n;
        cin >> s;
        vector<vector<int>> ftable(26, vector<int> (n, 0));
        vector<int> dis(n, 0);
        ftable[s[0]-'a'][0]++;
        ll cnt = 0;
        for(int i=1;i<n;++i) {
            for(int j=0;j<26;++j) {
                if(j != (s[i] - 'a'))ftable[j][i] = ftable[j][i-1];
                else ftable[j][i] = ftable[j][i-1] + 1;
            }
        }
        for(int i=0;i<n;++i) {
            ll cnt2 = 0;
            for(int j=0;j<26;++j) {
                // cout << ftable[j][i] << " ";
                if(ftable[j][i]) cnt2++;
                if(ftable[j][i] < ftable[j][n-1]) cnt2++;
            }
            // cout << endl;
            cnt = max(cnt, cnt2);
        }
        cout << cnt << endl;
    }
    return 0;
}