#include<bits/stdc++.h>
typedef long long   ll;
#define endl        '\n'
#define F           first
#define S           second
#define pb          push_back
#define yes         cout<<"YES\n"
#define no          cout<<"NO\n"
#define all(x)      x.begin(),x.end()
#define allr(x)     x.rbegin(),x.rend()
#define error1(x)   cerr<<#x<<" = "<<(x)<<endl
#define error2(a,b) cerr<<"("<<#a<<", "<<#b<<") = ("<<(a)<<", "<<(b)<<")\n";
#define coutall(v)  for(auto &it: v) cout<<it<<" "; cout<<endl;
#define _ASRafi__   ios::sync_with_stdio(false); cin.tie(0);
using namespace std;

void solve()
{
    ll n, ans = 0;
    string s1;
    cin >> n >> s1;
    vector<vector<ll>> pre(26, vector<ll> (n));
    for (int i = 0; i < n; i++)
    {
        pre[s1[i] - 'a'][i]++;
    }
    for(int i = 0; i < 26; i++)
    {
        for(int j = 1; j < n; j++)
        {
            pre[i][j] += pre[i][j - 1];
        }
    }
    for(int i = 1; i < n; i++)
    {
        for(int j = 0; j < 26; j++)
        {
            if(s1[i] - 'a' == j or pre[j][n - 1] == 0) continue;
            if(pre[j][i] == pre[j][n - 1] - pre[j][i]) 
            {
                ++ans;
                break;
            }
        }
    }
    cout << ans << endl;
    return;
}

int32_t main()
{
    _ASRafi__;
    int tc = 1;
    cin >> tc;
    for (int t = 1; t <= tc; t++)
    {
        // cout << "Case " << t << ": ";
        solve();
    }
    return 0;
}