Language: C++

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

#define rep(i, N) for (int i = 0; i < N; i++)
#define rep1(i, N) for (int i = 1; i <= N; i++)
const int intinf = numeric_limits<int>::max();

using ll = long long int;
using pii = pair<int, int>;
using pll = pair<ll, ll>;

#define MOD 1000000007

// Modulo.h start----------------------------------------

#pragma once

#include <vector>
#include <iostream>

unsigned int mod;
struct Modint;
std::vector<Modint> fact_mod;
std::vector<Modint> rev_fact_mod;

using namespace std;

template <typename Tint>
Tint gcd(Tint a, Tint b)
{
	// O(log max(a,b))
	a = abs(a);
	b = abs(b);
	return b != 0 ? gcd(b, a % b) : a;
}

template <typename Tint>
Tint lcm(Tint a, Tint b)
{
	return a / gcd(a, b) * b;
}

// a x + b y = gcd(a, b)
int extgcd(const unsigned int a, const unsigned int b, int &x, int &y)
{
	// O(log max(a,b))
	int g = a;
	x = 1;
	y = 0;
	if (b != 0)
		g = extgcd(b, a % b, y, x), y -= (a / b) * x;
	return g;
}

void set_mod(const unsigned int m)
{
	mod = m;
}
void set_mod(const int m)
{
	if (m > 0)
		set_mod((unsigned int)m);
	else
		std::cout << "Error in set_mod" << std::endl;
}

unsigned int inv_mod(const unsigned int a)
{
	int x, y;
	if (extgcd(a, mod, x, y) == 1)
		return (unsigned int)(((long long)x + mod) % mod);
	else // unsolvable
		return 0;
}

struct Modint
{
	unsigned int value;
	Modint() {}
	Modint(unsigned int value) : value(value % mod) {}
	Modint(int value) : Modint((unsigned int)(value % mod + mod)) {}
	Modint(unsigned long long value) : Modint((unsigned int)(value % mod)) {}
	Modint(long long value) : Modint((unsigned int)(value % mod + mod)) {}
	Modint(const Modint &rhs) : Modint(rhs.value) {}
	bool operator==(const Modint &rhs) const;
	inline bool operator!=(const Modint &rhs) const
	{
		return !(*this == rhs);
	}
	Modint &operator+=(const Modint &rhs);
	Modint &operator+=(const unsigned int rhs);
	Modint &operator+=(const int rhs);
	Modint &operator+=(const unsigned long long rhs);
	Modint &operator+=(const long long rhs);
	Modint &operator-=(const Modint &rhs);
	Modint &operator-=(const unsigned int rhs);
	Modint &operator-=(const int rhs);
	Modint &operator-=(const unsigned long long rhs);
	Modint &operator-=(const long long rhs);
	Modint &operator*=(const Modint &rhs);
	Modint &operator*=(const unsigned int rhs);
	Modint &operator*=(const int rhs);
	Modint &operator*=(const unsigned long long rhs);
	Modint &operator*=(const long long rhs);
	Modint &operator/=(const Modint &rhs);
	Modint &operator/=(const unsigned int rhs);
	Modint &operator/=(const int rhs);
	Modint &operator/=(const unsigned long long rhs);
	Modint &operator/=(const long long rhs);
};
bool Modint::operator==(const Modint &rhs) const
{
	return value == rhs.value;
}
Modint &Modint::operator+=(const unsigned int rhs)
{
	unsigned long long tmp = this->value;
	tmp += rhs;
	tmp %= mod;
	this->value = (unsigned int)tmp;
	return *this;
}
Modint &Modint::operator+=(const Modint &rhs)
{
	(*this) += rhs.value;
	return *this;
}
Modint &Modint::operator+=(const int rhs)
{
	(*this) += (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator+=(const unsigned long long rhs)
{
	(*this) += (unsigned int)(rhs % mod);
	return *this;
}
Modint &Modint::operator+=(const long long rhs)
{
	(*this) += (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator-=(const Modint &rhs)
{
	(*this) -= rhs.value;
	return *this;
}
Modint &Modint::operator-=(const unsigned int rhs)
{
	*this += mod - rhs % mod;
	return *this;
}
Modint &Modint::operator-=(const int rhs)
{
	*this -= (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator-=(const unsigned long long rhs)
{
	(*this) -= (unsigned int)(rhs % mod);
	return *this;
}
Modint &Modint::operator-=(const long long rhs)
{
	(*this) -= (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator*=(const Modint &rhs)
{
	(*this) *= rhs.value;
	return *this;
}
Modint &Modint::operator*=(const unsigned int rhs)
{
	unsigned long long tmp = this->value;
	tmp *= rhs;
	tmp %= mod;
	this->value = (unsigned int)tmp;
	return *this;
}
Modint &Modint::operator*=(const int rhs)
{
	(*this) *= (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator*=(const unsigned long long rhs)
{
	(*this) *= (unsigned int)(rhs % mod);
	return *this;
}
Modint &Modint::operator*=(const long long rhs)
{
	(*this) *= (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator/=(const Modint &rhs)
{
	(*this) /= rhs.value;
	return *this;
}
Modint &Modint::operator/=(const unsigned int rhs)
{
	*this *= inv_mod(rhs);
	return *this;
}
Modint &Modint::operator/=(const int rhs)
{
	*this /= (unsigned int)(rhs % mod + mod);
	return *this;
}
Modint &Modint::operator/=(const unsigned long long rhs)
{
	*this /= (unsigned int)(rhs % mod);
	return *this;
}
Modint &Modint::operator/=(const long long rhs)
{
	*this /= (unsigned int)(rhs % mod + mod);
	return *this;
}
const Modint operator+(const Modint &lhs, const Modint &rhs)
{
	return Modint(lhs) += rhs;
}
const Modint operator+(const Modint &lhs, unsigned int rhs)
{
	return Modint(lhs) += rhs;
}
const Modint operator+(unsigned int lhs, const Modint &rhs)
{
	return Modint(lhs) += rhs;
}
const Modint operator-(const Modint &lhs, const Modint &rhs)
{
	return Modint(lhs) -= rhs;
}
const Modint operator-(const Modint &lhs, unsigned int rhs)
{
	return Modint(lhs) -= rhs;
}
const Modint operator-(unsigned int lhs, const Modint &rhs)
{
	return Modint(lhs) -= rhs;
}
const Modint operator*(const Modint &lhs, const Modint &rhs)
{
	return Modint(lhs) *= rhs;
}
const Modint operator*(const Modint &lhs, unsigned int rhs)
{
	return Modint(lhs) *= rhs;
}
const Modint operator*(unsigned int lhs, const Modint &rhs)
{
	return Modint(lhs) *= rhs;
}
const Modint operator/(const Modint &lhs, const Modint &rhs)
{
	return Modint(lhs) /= rhs;
}
const Modint operator/(const Modint &lhs, unsigned int rhs)
{
	return Modint(lhs) /= rhs;
}
const Modint operator/(unsigned int lhs, const Modint &rhs)
{
	return Modint(lhs) /= rhs;
}
ostream &operator<<(std::ostream &lhs, const Modint &rhs)
{
	lhs << rhs.value;
	return lhs;
}

Modint pow_mod(const Modint &x, const unsigned int k)
{ //x^k (mod)
	if (k == 0)
		return Modint(1);
	if (k % 2 == 0)
		return pow_mod(x * x, k / 2);
	else
		return x * pow_mod(x, k - 1);
}
Modint pow_mod(const unsigned int x, const unsigned int k)
{
	return pow_mod(Modint(x), k);
}

std::vector<Modint> set_fact_mod(unsigned int n)
{
	// O(n)
	fact_mod = vector<Modint>(n + 1);
	fact_mod[0] = 1;
	for (unsigned int i = 1; i <= n; i++)
	{
		fact_mod[i] = fact_mod[i - 1] * i;
	}
	return fact_mod;
}

std::vector<Modint> set_rev_fact_mod(unsigned int n)
{
	// O(n)
	rev_fact_mod = vector<Modint>(n + 1);
	rev_fact_mod[n] = 1 / fact_mod[n];
	for (int i = n - 1; i >= 0; i--)
	{
		rev_fact_mod[i] = rev_fact_mod[i + 1] * (unsigned int)(i + 1);
	}
	return rev_fact_mod;
}

Modint combination_mod_precalculation(unsigned int n, unsigned int r)
{
	//set_mod, fact_mod, rev_fact_mod
	return fact_mod[n] * rev_fact_mod[r] * rev_fact_mod[n - r];
}

Modint combination_mod_straightforward(unsigned long long n, unsigned long long r)
{ //mod is prime, O(sqrt(n))
	if (r * 2 > n)
		r = n - r;
	Modint numerator = 1;
	Modint denominator = 1;
	for (unsigned long long i = 1; i <= r; ++i)
	{
		numerator *= n - i + 1;
		denominator *= i;
	}
	return numerator / denominator;
}

// Modulo.h end----------------------------------------------

void solve()
{
    int n, k;
    cin >> n >> k;

    Modint ans = 0;

    set_mod(MOD);
    set_fact_mod(n);
    set_rev_fact_mod(n);
    rep(i, m)
    {
        ans += combination_mod_precalculation(n, m) * combination_mod_precalculation(n - 1, m);
    }

    cout << ans << endl;
}

int main()
{
    solve();
    return 0;
}

Compiler output:
a.cc:16:9: warning: #pragma once in main file
   16 | #pragma once
      |         ^~~~
a.cc: In function 'void solve()':
a.cc:345:12: error: 'm' was not declared in this scope
  345 |     rep(i, m)
      |            ^
a.cc:4:39: note: in definition of macro 'rep'
    4 | #define rep(i, N) for (int i = 0; i < N; i++)
      |                                       ^