Codeforces-SolutionsA/Codes/1905C Largest Subsequence/1905C.cpp

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

// Short forms
#define int                 long long
#define ll                  long long
#define endl                '\n'
#define ff                  first
#define ss                  second
#define pb                  push_back
#define all(x)              x.begin(), x.end()
#define sz(x)               (int)(x).size()

// Outputs
#define yes                 cout<<"YES"<<endl
#define no                  cout<<"NO"<<endl

// Constants
#define PI                  3.141592653589793238
#define INF                 LONG_LONG_MAX
#define MOD                 1e9+7

// Faster Input Output
#define FAST_IO             (ios_base:: sync_with_stdio(false),cin.tie(NULL));

// Maths
ll fact(ll n)          { if(n==0) return 1; ll res = 1; for (ll i = 2; i <= n; i++) res = res * i; return res; }
ll nPr(ll n, ll r)     { return fact(n) / fact(n - r); }
ll nCr(ll n, ll r)     { return fact(n) / (fact(r) * fact(n - r)); }
ll gcd(ll a, ll b)     { if (b == 0) return a; return gcd(b, a % b); }
ll lcm(ll a, ll b)     { return (a * b) / gcd(a, b);}
ll mypow(ll a, ll b)   { ll ans = 1; while(b){ if (b&1) ans = (ans*a) ; b /= 2; a = (a*a); } return ans; }
bool isPrime(ll n)     { if(n <= 1) return false; for(ll i = 2; i <= sqrt(n); i++) if(n % i == 0) return false; return true; }

//Debugging
#ifndef ONLINE_JUDGE
#define dbg(x) cerr << #x <<" "; _print(x); cerr << endl;
#define dbgin(x) cerr << #x <<" "; _print(x); cerr << ";"<<endl;
#else
#define dbg(x)
#define dbgin(x)
#endif
 
void _print(int t) {cerr << t;}void _print(string t) {cerr << t;}void _print(char t) {cerr << t;}
void _print(long double t) {cerr << t;}void _print(double t) {cerr << t;}void _print(unsigned ll t) {cerr << t;}
template <class T, class V> void _print(pair <T, V> p);
template <class T> void _print(vector <T> v);template <class T> void _print(set <T> v);
template <class T, class V> void _print(map <T, V> v);template <class T> void _print(multiset <T> v);
template <class T, class V> void _print(pair <T, V> p) {cerr << "{"; _print(p.first); cerr << ","; _print(p.second); cerr << "}";}
template <class T> void _print(vector <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(set <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(multiset <T> v) {cerr << "[ "; for (T i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T> void _print(unordered_set <T> v) {cerr<<"[ "; for(T i : v) {_print(i); cerr<<" ";} cerr<<"]";}
template <class T, class V> void _print(map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}
template <class T, class V> void _print(multimap <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";} 
template <class T, class V> void _print(unordered_map <T, V> v) {cerr << "[ "; for (auto i : v) {_print(i); cerr << " ";} cerr << "]";}

/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

bool cmp(pair<char,int>a, pair<char,int>b)
{
    if(a.ff==b.ff)
        return a.ss<b.ss;
    return a.ff>b.ff;
}

void solve()
{
    int n;
    string s;
    cin>>n>>s;
    vector<int>v;
    for(int i=0; i<sz(s); ++i)
    {
        while(!v.empty() && s[v.back()]<s[i])
            v.pop_back();
        v.pb(i);
    }
    int ct=count(all(s),s[v[0]]);
    for(int i=0; i<sz(v)/2; ++i)
    {
        swap(s[v[i]],s[v[sz(v)-i-1]]);
    }
    int sorted=1;
    for(int i=1;i<sz(s);++i)
    {
        if(s[i]<s[i-1])
        {
            sorted=0;
            break;
        }
    }
    if(sorted)
        cout<<sz(v)-ct<<endl;
    else
        cout<<-1<<endl;
}

int32_t main()
{
    FAST_IO;
    int TC = 1;
    cin >> TC;
    while (TC--) solve();
}