# | Time | Username | Problem | Language | Result | Execution time | Memory |
---|---|---|---|---|---|---|---|
890577 | fanwen | NoM (RMI21_nom) | C++17 | 2 ms | 1116 KiB |
This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define ll long long
#define file(name) \
if(fopen(name".inp", "r")) \
freopen(name".inp", "r", stdin), freopen(name".out", "w", stdout);
template <int Mod>
struct Modular {
private :
int val;
static int inverse(int a, int b) {
a %= b;
assert(a);
if(a == 1) return 1;
return int(b - (long long) inverse(b, a) * (long long) b / a);
}
public :
Modular(long long x = 0) : val(x % Mod) { if(val < 0) val += Mod; }
friend bool operator == (const Modular &a, const Modular &b) { return a.val == b.val; }
friend bool operator != (const Modular &a, const Modular &b) { return a.val != b.val; }
Modular& operator = (const long long &x) { val = x % Mod; if(val < 0) val += Mod; return *this; }
Modular& operator = (const Modular &x) { val = x.val; return *this; }
friend istream & operator >> (istream &in, Modular &a) { long long x; in >> x; a = Modular(x); return in; }
friend ostream & operator << (ostream &out, const Modular &a) { return out << a.val; }
explicit operator int() const { return val; }
explicit operator bool() const { return val > 0; }
Modular inv() const {
Modular res;
res.val = inverse(val, Mod);
return res;
}
Modular operator ++() { (*this) += 1; return *this; }
Modular operator --() { (*this) -= 1; return *this; }
Modular operator ++(int) { (*this) += 1; return *this - 1; }
Modular operator --(int) { (*this) -= 1; return *this + 1; }
Modular operator + () const { return *this; }
Modular operator - () const {
Modular res;
res.val = (val ? Mod - val : 0);
return res;
}
Modular& operator += (const Modular &a) {
val += a.val;
if(val >= Mod) val -= Mod;
return *this;
}
Modular& operator -= (const Modular &a) {
val -= a.val;
if(val < 0) val += Mod;
return *this;
}
Modular& operator *= (const Modular &a) {
val = 1LL * val * a.val % Mod;
return *this;
}
Modular& operator /= (const Modular &a) {
(*this) *= a.inv();
return *this;
}
friend Modular operator + (const Modular &a, const Modular &b) { return Modular(a) += b; }
friend Modular operator - (const Modular &a, const Modular &b) { return Modular(a) -= b; }
friend Modular operator * (const Modular &a, const Modular &b) { return Modular(a) *= b; }
friend Modular operator / (const Modular &a, const Modular &b) { return Modular(a) /= b; }
};
// const int Mod = 998244353;
// const int Mod = 1e9 + 9; // 1000000009
const int Mod = 1e9 + 7; // 1000000007
using Modint = Modular <Mod>;
template <class T> T pow(T a, long long b) {
T ans = 1, mul = a;
for (; b; b >>= 1) {
if(b & 1LL) ans *= mul;
mul *= mul;
}
return ans;
}
const int Max_size = 1e5 + 5;
Modint fact[Max_size + 5], invs[Max_size + 5];
void prepare_Comb() {
fact[0] = invs[0] = 1;
for (int i = 1; i <= Max_size; ++i) fact[i] = fact[i - 1] * i;
invs[Max_size] = fact[Max_size].inv();
for (int i = Max_size - 1; i >= 1; --i) invs[i] = invs[i + 1] * (i + 1);
}
Modint C(int n, int k) {
if(n < k || k < 0) return 0;
return fact[n] * invs[k] * invs[n - k];
}
Modint A(int n, int k) {
if(n < k || k < 0) return 0;
return fact[n] * invs[n - k];
}
const int MAX = 2e3 + 5;
int N, M;
Modint dp[2 * MAX];
void you_make_it(void) {
cin >> N >> M;
dp[0] = 1;
for (int i = 0; i < M; ++i) {
int len = (2 * N - i) / M;
for (int s = N; s >= 1; --s) {
for (int j = 1; 2 * j <= len && j <= s; ++j) {
dp[s] += dp[s - j] * A(len, 2 * j) * C(s, j);
}
}
}
// for (int i = 0; i <= N; ++i) cout << dp[i] << " "; cout << '\n';
Modint ans = 0;
for (int i = 0; i <= N; ++i) ans += dp[i] * (i & 1 ? - 1 : 1) * fact[2 * N - 2 * i] * C(N, i);
cout << ans;
}
signed main() {
#ifdef LOCAL
freopen("TASK.inp", "r", stdin);
freopen("TASK.out", "w", stdout);
#endif
file("nom");
auto start_time = chrono::steady_clock::now();
cin.tie(0), cout.tie(0) -> sync_with_stdio(0);
prepare_Comb();
you_make_it();
auto end_time = chrono::steady_clock::now();
cerr << "\nExecution time : " << chrono::duration_cast <chrono::milliseconds> (end_time - start_time).count() << "[ms]" << endl;
return (0 ^ 0);
}
// Dream it. Wish it. Do it.
Compilation message (stderr)
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