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F.cpp
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F.cpp
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#define DEBUG 1
/**
* File : F.cpp
* Author : Kazune Takahashi
* Created : 2019/11/5 22:01:12
* Powered by Visual Studio Code
*/
#include <iostream>
#include <iomanip>
#include <algorithm>
#include <vector>
#include <string>
#include <complex>
#include <tuple>
#include <queue>
#include <stack>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <functional>
#include <random>
#include <chrono>
#include <cctype>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <cstdlib>
using namespace std;
template <typename T>
void ch_max(T &left, T right)
{
if (left < right)
{
left = right;
}
}
template <typename T>
void ch_min(T &left, T right)
{
if (left > right)
{
left = right;
}
}
using ll = long long;
class mint
{
public:
static ll MOD;
ll x;
mint() : x(0) {}
mint(ll x) : x(x % MOD) {}
mint operator-() const { return x ? MOD - x : 0; }
mint &operator+=(const mint &a)
{
if ((x += a.x) >= MOD)
{
x -= MOD;
}
return *this;
}
mint &operator-=(const mint &a) { return *this += -a; }
mint &operator*=(const mint &a)
{
(x *= a.x) %= MOD;
return *this;
}
mint &operator/=(const mint &a)
{
mint b{a};
return *this *= b.power(MOD - 2);
}
mint operator+(const mint &a) const { return mint(*this) += a; }
mint operator-(const mint &a) const { return mint(*this) -= a; }
mint operator*(const mint &a) const { return mint(*this) *= a; }
mint operator/(const mint &a) const { return mint(*this) /= a; }
bool operator<(const mint &a) const { return x < a.x; }
bool operator==(const mint &a) const { return x == a.x; }
const mint power(ll N)
{
if (N == 0)
{
return 1;
}
else if (N % 2 == 1)
{
return *this * power(N - 1);
}
else
{
mint half = power(N / 2);
return half * half;
}
}
};
ll mint::MOD = 998244353;
istream &operator>>(istream &stream, mint &a) { return stream >> a.x; }
ostream &operator<<(ostream &stream, const mint &a) { return stream << a.x; }
class combination
{
public:
vector<mint> inv, fact, factinv;
static int MAX_SIZE;
combination() : inv(MAX_SIZE), fact(MAX_SIZE), factinv(MAX_SIZE)
{
inv[1] = 1;
for (auto i = 2; i < MAX_SIZE; i++)
{
inv[i] = (-inv[mint::MOD % i]) * (mint::MOD / i);
}
fact[0] = factinv[0] = 1;
for (auto i = 1; i < MAX_SIZE; i++)
{
fact[i] = mint(i) * fact[i - 1];
factinv[i] = inv[i] * factinv[i - 1];
}
}
mint operator()(int n, int k)
{
if (n >= 0 && k >= 0 && n - k >= 0)
{
return fact[n] * factinv[k] * factinv[n - k];
}
return 0;
}
};
int combination::MAX_SIZE = 20000010;
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }
// constexpr double epsilon = 1e-10;
// constexpr ll infty = 1000000000000000LL;
// constexpr int dx[4] = {1, 0, -1, 0};
// constexpr int dy[4] = {0, 1, 0, -1};
void Yes()
{
cout << "Yes" << endl;
exit(0);
}
void No()
{
cout << "No" << endl;
exit(0);
}
combination C;
mint catalan(ll x, ll y)
{
return C(x + y, y) - C(x + y, y - 1);
}
int main()
{
ll N, A, B;
cin >> N >> A >> B;
ll M{min({A, N - B, B - 1})};
mint ans{0};
if (B == 0)
{
cout << 1 << endl;
return 0;
}
ll X{B};
ll D{B - A};
for (auto Y = 0LL; Y <= M; Y++)
{
mint tmp{catalan(X - 1, Y)};
if (X + Y == N && Y == A)
{
ans += tmp;
}
else
{
ll Z{N - X - Y};
ans += tmp * C(X - Y - D + Z - 1 - 1, X - Y - D - 1);
}
}
cout << ans << endl;
}