#include<bits/stdc++.h>
using namespace std;
//ofstream filee("output8.txt");
//ifstream file("input8.txt");
void solve()
{
    //string s;
    //while(file >> s)
    
    int n; cin>>n;
    string s; cin>>s;
    int a[n][26]={0};
    int b[26]={0};

    for(int i=0;i<n;i++)
    {
        b[s[i]-'a']++;
        for(int j=0;j<26;j++)
        {
            a[i][j]=b[j];
        }
    }

    int ans=0;

    for(int i=0;i<n;i++)
    {
        int point = s[i]-'a';
        for(int j=0;j<26;j++)
        {
            if(j==point) continue;
            if(a[i][j]!=0 && a[i][j]*2==b[j])
            {
                ans++;
                break;
            }
        }
    }

    //filee<<ans<<endl;
    cout<<ans<<endl;
    //cout<<s<<endl;
    
}
int main(){
    
    int t; cin>>t; while(t--) solve();
    //file.close();
    //filee.close();
    }