Language: C++

//c++ -std=gnu++14 a.cpp
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <iostream>
#include <istream>
#include <iterator>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
#include <tuple>
#include <iomanip>
#include <climits>
#include <fstream>
#include <random>
#include <atcoder/all>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
//typedef pair<ll, ll> P;
#define rep(i, n) for(int i = 0; i < (n); i++)
#define revrep(i, n) for(int i = (n)-1; i >= 0; i--)
#define pb push_back
#define f first
#define s second
#define chmin(x, y) x = min(x, y);
#define chmax(x, y) x = max(x, y);
#define len(x) ((int)(x).size())

//const ll INFL = LLONG_MAX;//10^18 = 2^60
const ll INFL = 1LL<<60;
//const int INF = INT_MAX;
const int INF = 1 << 30;//10^9
//const ll MOD = 1000000007;
const ll MOD = 998244353;
double EPS = 1e-10;

vector<ll> dy = {0, 1, 0, -1, 1, 1, -1, -1, 0};
vector<ll> dx = {1, 0, -1, 0, 1, -1, 1, -1, 0};

void pres(double A){printf("%.9lf\n", A);}
void BinarySay(ll x, ll y = 60){rep(i, y) cout << (x>>(y-1-i) & 1); cout << endl;}
ll cnt_bit(ll x){return __builtin_popcountll(x);}

template<typename __T__>
void vecout(vector<__T__> x){rep(i, len(x)){cout<<x[i]<<" ";}cout << endl;}

ll pow_long(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x; k /= 2;
  }
  return res;
}

ll pow_mod(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}

ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}

ll lcm(ll x, ll y){
  ll res = x / gcd(x, y);
  res *= y;
  return res;
};


//コンビネーション
const int MAXcomb = 2000010;
ll fac[MAXcomb], finv[MAXcomb], inv[MAXcomb];
//facはn!,finvは1/n!
//invは逆元
void COMinit(){
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for(int i = 2; i < MAXcomb; i++){
        fac[i] = fac[i-1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD/i) % MOD;
        finv[i] = finv[i-1] * inv[i] % MOD;
    }
}
ll comb(int n, int k){
    if(n < k) return 0;
    if(n < 0 || k < 0) return 0;
    return fac[n] * finv[k] % MOD * finv[n-k] % MOD;
}

ll disit(ll s, ll base = 10){
  ll res = 0;
  while(s){
    res++;
    s /= base;
  }
  return res;
}

ll kaikai[100010];
void make_kaikai(){
  kaikai[0] = 1;
  kaikai[1] = 1;
  for(int i = 2; i < 100010; i++){
    kaikai[i] = kaikai[i-2] * i % MOD;
  }
}

ll N;
ll h[100010];
ll cnt[100010];
vector<ll> A;

vector<ll> merge(vector<vector<ll>>& B){
  int n = len(B);
  if(n == 1){
    return B[0];
  }
  vector<vector<ll>> L, R;
  rep(i, n){
    if(i & 1) L.pb(B[i]);
    else R.pb(B[i]);
  }
  vector<ll> left = merge(L);
  vector<ll> right = merge(R);
  vector<ll> res = atcoder::convolution(left, right);
  return res;
}

void solve(){
  COMinit();
  make_kaikai();
  cin >> N;
  rep(i, 2*N) cin >> h[i];
  rep(i, 2*N) cnt[h[i]]++;

  rep(i, 100010){
    if(cnt[i] != 0) A.pb(cnt[i]);
  }


  vector<vector<ll>> B;
  rep(i, len(A)){
    vector<ll> a;
    rep(j, A[i]/2+1){
      //jペア
      a.pb(comb(A[i], 2*j) * kaikai[max(2*j-1, 0)]);
    }
    B.pb(a);
  }
  vector<ll> C = merge(B);

  ll ans = 0;
  rep(i, len(C)){
    if(i & 1) ans += MOD - C[i] * kaikai[2*N-i*2-1] % MOD;
    else ans += C[i] * kaikai[2*N-i*2-1] % MOD;
    ans %= MOD;
  }
  cout << ans << endl;
}

int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  solve();
}


Compiler output:
a.cc:20:10: fatal error: atcoder/all: No such file or directory
   20 | #include <atcoder/all>
      |          ^~~~~~~~~~~~~
compilation terminated.