Problem:
Score : 600 points

Problem Statement

There are 2N people numbered 1 through 2N.
The height of Person i is h_i.

How many ways are there to make N pairs of people such that the following conditions are satisfied?
Compute the answer modulo 998,244,353.

Each person is contained in exactly one pair.

For each pair, the heights of the two people in the pair are different.

Two ways are considered different if for some p and q, Person p and Person q are paired in one way and not in the other.

Constraints

1 \leq N \leq 50,000

1 \leq h_i \leq 100,000

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N
h_1
:
h_{2N}

Output

Print the answer.

Sample Input 1

2
1
1
2
3

Sample Output 1

2

There are two ways:

Form the pair (Person 1, Person 3) and the pair (Person 2, Person 4).

Form the pair (Person 1, Person 4) and the pair (Person 2, Person 3).

Sample Input 2

5
30
10
20
40
20
10
10
30
50
60

Sample Output 2

516

Solution in Rust (1.42.0) (judge verdict: Accepted)

// ---------- begin ModInt ----------
mod modint {

    #[allow(dead_code)]
    pub struct Mod;
    impl ConstantModulo for Mod {
        const MOD: u32 = 1_000_000_007;
    }

    #[allow(dead_code)]
    pub struct StaticMod;
    static mut STATIC_MOD: u32 = 0;
    impl Modulo for StaticMod {
        fn modulo() -> u32 {
            unsafe { STATIC_MOD }
        }
    }

    #[allow(dead_code)]
    impl StaticMod {
        pub fn set_modulo(p: u32) {
            unsafe {
                STATIC_MOD = p;
            }
        }
    }

    use std::marker::*;
    use std::ops::*;

    pub trait Modulo {
        fn modulo() -> u32;
    }

    pub trait ConstantModulo {
        const MOD: u32;
    }

    impl<T> Modulo for T
    where
        T: ConstantModulo,
    {
        fn modulo() -> u32 {
            T::MOD
        }
    }

    pub struct ModInt<T>(pub u32, PhantomData<T>);

    impl<T> Clone for ModInt<T> {
        fn clone(&self) -> Self {
            ModInt::new_unchecked(self.0)
        }
    }

    impl<T> Copy for ModInt<T> {}

    impl<T: Modulo> Add for ModInt<T> {
        type Output = ModInt<T>;
        fn add(self, rhs: Self) -> Self::Output {
            let mut d = self.0 + rhs.0;
            if d >= T::modulo() {
                d -= T::modulo();
            }
            ModInt::new_unchecked(d)
        }
    }

    impl<T: Modulo> AddAssign for ModInt<T> {
        fn add_assign(&mut self, rhs: Self) {
            *self = *self + rhs;
        }
    }

    impl<T: Modulo> Sub for ModInt<T> {
        type Output = ModInt<T>;
        fn sub(self, rhs: Self) -> Self::Output {
            let mut d = T::modulo() + self.0 - rhs.0;
            if d >= T::modulo() {
                d -= T::modulo();
            }
            ModInt::new_unchecked(d)
        }
    }

    impl<T: Modulo> SubAssign for ModInt<T> {
        fn sub_assign(&mut self, rhs: Self) {
            *self = *self - rhs;
        }
    }

    impl<T: Modulo> Mul for ModInt<T> {
        type Output = ModInt<T>;
        fn mul(self, rhs: Self) -> Self::Output {
            let v = self.0 as u64 * rhs.0 as u64 % T::modulo() as u64;
            ModInt::new_unchecked(v as u32)
        }
    }

    impl<T: Modulo> MulAssign for ModInt<T> {
        fn mul_assign(&mut self, rhs: Self) {
            *self = *self * rhs;
        }
    }

    impl<T: Modulo> Neg for ModInt<T> {
        type Output = ModInt<T>;
        fn neg(self) -> Self::Output {
            if self.0 == 0 {
                Self::zero()
            } else {
                Self::new_unchecked(T::modulo() - self.0)
            }
        }
    }

    impl<T> std::fmt::Display for ModInt<T> {
        fn fmt<'a>(&self, f: &mut std::fmt::Formatter<'a>) -> std::fmt::Result {
            write!(f, "{}", self.0)
        }
    }

    impl<T: Modulo> std::str::FromStr for ModInt<T> {
        type Err = std::num::ParseIntError;
        fn from_str(s: &str) -> Result<Self, Self::Err> {
            let val = s.parse::<u32>()?;
            Ok(ModInt::new(val))
        }
    }

    impl<T: Modulo> From<usize> for ModInt<T> {
        fn from(val: usize) -> ModInt<T> {
            ModInt::new_unchecked((val % T::modulo() as usize) as u32)
        }
    }

    impl<T: Modulo> From<u64> for ModInt<T> {
        fn from(val: u64) -> ModInt<T> {
            ModInt::new_unchecked((val % T::modulo() as u64) as u32)
        }
    }

    impl<T: Modulo> From<i64> for ModInt<T> {
        fn from(val: i64) -> ModInt<T> {
            let m = T::modulo() as i64;
            ModInt::new((val % m + m) as u32)
        }
    }

    #[allow(dead_code)]
    impl<T> ModInt<T> {
        pub fn new_unchecked(d: u32) -> Self {
            ModInt(d, PhantomData)
        }
        pub fn zero() -> Self {
            ModInt::new_unchecked(0)
        }
        pub fn one() -> Self {
            ModInt::new_unchecked(1)
        }
        pub fn is_zero(&self) -> bool {
            self.0 == 0
        }
    }

    #[allow(dead_code)]
    impl<T: Modulo> ModInt<T> {
        pub fn new(d: u32) -> Self {
            ModInt::new_unchecked(d % T::modulo())
        }
        pub fn pow(&self, mut n: u64) -> Self {
            let mut t = Self::one();
            let mut s = *self;
            while n > 0 {
                if n & 1 == 1 {
                    t *= s;
                }
                s *= s;
                n >>= 1;
            }
            t
        }
        pub fn inv(&self) -> Self {
            assert!(self.0 != 0);
            self.pow(T::modulo() as u64 - 2)
        }
    }

    #[allow(dead_code)]
    pub fn mod_pow(r: u64, mut n: u64, m: u64) -> u64 {
        let mut t = 1 % m;
        let mut s = r % m;
        while n > 0 {
            if n & 1 == 1 {
                t = t * s % m;
            }
            s = s * s % m;
            n >>= 1;
        }
        t
    }
}
// ---------- end ModInt ----------
// ---------- begin Precalc ----------
mod precalc {
    use super::modint::*;
    #[allow(dead_code)]
    pub struct Precalc<T> {
        inv: Vec<ModInt<T>>,
        fact: Vec<ModInt<T>>,
        ifact: Vec<ModInt<T>>,
    }
    #[allow(dead_code)]
    impl<T: Modulo> Precalc<T> {
        pub fn new(n: usize) -> Precalc<T> {
            let mut inv = vec![ModInt::one(); n + 1];
            let mut fact = vec![ModInt::one(); n + 1];
            let mut ifact = vec![ModInt::one(); n + 1];
            for i in 2..(n + 1) {
                fact[i] = fact[i - 1] * ModInt::new_unchecked(i as u32);
            }
            ifact[n] = fact[n].inv();
            if n > 0 {
                inv[n] = ifact[n] * fact[n - 1];
            }
            for i in (1..n).rev() {
                ifact[i] = ifact[i + 1] * ModInt::new_unchecked((i + 1) as u32);
                inv[i] = ifact[i] * fact[i - 1];
            }
            Precalc {
                inv: inv,
                fact: fact,
                ifact: ifact,
            }
        }
        pub fn inv(&self, n: usize) -> ModInt<T> {
            assert!(n > 0);
            self.inv[n]
        }
        pub fn fact(&self, n: usize) -> ModInt<T> {
            self.fact[n]
        }
        pub fn ifact(&self, n: usize) -> ModInt<T> {
            self.ifact[n]
        }
        pub fn perm(&self, n: usize, k: usize) -> ModInt<T> {
            if k > n {
                return ModInt::zero();
            }
            self.fact[n] * self.ifact[n - k]
        }
        pub fn comb(&self, n: usize, k: usize) -> ModInt<T> {
            if k > n {
                return ModInt::zero();
            }
            self.fact[n] * self.ifact[k] * self.ifact[n - k]
        }
    }
}
// ---------- end Precalc ----------
// ---------- begin NTT ----------
#[allow(dead_code)]
mod transform {
    use super::modint::*;
    pub trait NTTFriendly: ConstantModulo {
        fn order() -> usize;
        fn zeta() -> u32;
    }
    pub fn ntt<T: NTTFriendly>(f: &mut [ModInt<T>]) {
        let n = f.len();
        assert!(n.count_ones() == 1);
        assert!(n <= T::order());
        let len = n.trailing_zeros() as usize;
        let mut zeta = Vec::with_capacity(len);
        let mut r = ModInt::new_unchecked(T::zeta()).pow((T::order() >> len) as u64);
        for _ in 0..len {
            zeta.push(r);
            r = r * r;
        }
        for (k, &z) in zeta.iter().rev().enumerate().rev() {
            let m = 1 << k;
            for f in f.chunks_exact_mut(2 * m) {
                let mut q = ModInt::one();
                let (x, y) = f.split_at_mut(m);
                for (x, y) in x.iter_mut().zip(y.iter_mut()) {
                    let a = *x;
                    let b = *y;
                    *x = a + b;
                    *y = (a - b) * q;
                    q *= z;
                }
            }
        }
    }
    pub fn intt<T: NTTFriendly>(f: &mut [ModInt<T>]) {
        let n = f.len();
        assert!(n.count_ones() == 1);
        assert!(n <= T::order());
        let len = n.trailing_zeros() as usize;
        let mut zeta = Vec::with_capacity(len);
        let mut r = ModInt::new_unchecked(T::zeta()).inv().pow((T::order() >> len) as u64);
        for _ in 0..len {
            zeta.push(r);
            r = r * r;
        }
        for (k, &z) in zeta.iter().rev().enumerate() {
            let m = 1 << k;
            for f in f.chunks_exact_mut(2 * m) {
                let mut q = ModInt::one();
                let (x, y) = f.split_at_mut(m);
                for (x, y) in x.iter_mut().zip(y.iter_mut()) {
                    let a = *x;
                    let b = *y * q;
                    *x = a + b;
                    *y = a - b;
                    q *= z;
                }
            }
        }
        let ik = ModInt::new_unchecked((T::MOD + 1) >> 1).pow(len as u64);
        for f in f.iter_mut() {
            *f *= ik;
        }
    }
    pub fn multiply<T: NTTFriendly>(a: &[ModInt<T>], b: &[ModInt<T>]) -> Vec<ModInt<T>> {
        if a.is_empty() || b.is_empty() {
            return vec![];
        }
        let n = a.len() + b.len() - 1;
        let k = n.next_power_of_two();
        assert!(k <= T::order());
        let mut f = Vec::with_capacity(k);
        let mut g = Vec::with_capacity(k);
        f.extend_from_slice(a);
        f.resize(k, ModInt::zero());
        ntt(&mut f);
        g.extend_from_slice(b);
        g.resize(k, ModInt::zero());
        ntt(&mut g);
        for (f, g) in f.iter_mut().zip(g.iter()) {
            *f *= *g;
        }
        intt(&mut f);
        f.truncate(n);
        f
    }
}
// ---------- end NTT ----------

use proconio::*;

use modint::*;

struct P;
impl ConstantModulo for P {
    const MOD: u32 = 998_244_353;
}

impl transform::NTTFriendly for P {
    fn order() -> usize {
        1 << 23
    }
    fn zeta() -> u32 {
        let p = Self::MOD as u64;
        mod_pow(3, (p - 1) >> 23, p) as u32
    }
}

type M = ModInt<P>;

fn calc(a: &[Vec<M>]) -> Vec<M> {
    if a.len() == 1 {
        a[0].clone()
    } else {
        let m = a.len() / 2;
        let (l, r) = a.split_at(m);
        transform::multiply(&calc(l), &calc(&r))
    }
}

#[fastout]
fn run() {
    input! {
        n: usize,
        h: [usize; 2 * n],
    }
    let w = 100_000;
    let mut cnt = vec![0; w + 1];
    for h in h {
        cnt[h] += 1;
    }
    let pc = precalc::Precalc::new(w + 1);
    let mut memo = vec![vec![M::one()]];
    for c in cnt {
        if c < 2 {
            continue;
        }
        let mut a = vec![M::one()];
        for i in 1.. {
            if i * 2 > c {
                break;
            }
            a.push(pc.comb(c, 2 * i) * pc.fact(2 * i) * M::new(2).inv().pow(i as u64) * pc.ifact(i));
        }
        memo.push(a);
    }
    let a = calc(&memo);
    let mut ans = M::zero();
    let mut sign = M::one();
    for (i, a) in a.into_iter().enumerate() {
        ans += sign * a * pc.fact(2 * n - 2 * i) * pc.inv(2).pow((n - i) as u64) * pc.ifact(n - i);
        sign = -sign;
    }
    println!("{}", ans);
}

fn main() {
    run();
}