Language: C++

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

#line 1 "math/ModInt.cpp"
/**
 * @title ModInt
 * @brief mod を取りながら計算する。リテラル型の要件を満たし、constexprに対応している。
 * @brief これでも Verify してます。 https://github.com/spihill/library/blob/master/test/mytest/ModInt.test.cpp
 */
namespace modint_n {
using value_type = signed;
template<value_type mod>
struct ModInt {
	using i64 = int_fast64_t;
	value_type x;
	constexpr static value_type get_mod() {
		return mod;
	}
	constexpr ModInt(i64 x_) : x(mod_(x_)) {}
	constexpr ModInt() : ModInt(0) {}
	~ModInt() = default;
	inline constexpr ModInt& operator+=(const ModInt rhs) {
		i64 t = static_cast<i64>(x) + rhs.x;
		if (t >= mod) x = t - mod;
		else x = t;
		return (*this);
	}
	inline constexpr ModInt& operator-=(const ModInt rhs) {
		i64 t = static_cast<i64>(x) + mod - rhs.x;
		if (t >= mod) x = t - mod;
		else x = t;
		return *this;
	}
	inline constexpr ModInt& operator*=(const ModInt rhs) {
		x = static_cast<i64>(x) * rhs.x % mod;
		return *this;
	}
	inline constexpr ModInt& operator/=(ModInt rhs) {
		return *this *= rhs.inv();
	}
	inline constexpr ModInt power(i64 p) const {
		ModInt res = 1;
		ModInt a = x;
		for (; p; res = p & 1 ? res * a : res, a *= a, p >>= 1);
		return res;
	}
	inline constexpr ModInt inv() const {
		value_type z = 0, w = 0;
		extgcd(mod, x, z, w);
		return ModInt(w);
	}
	inline constexpr ModInt& operator=(const ModInt& rhs) {
		this->x = rhs.x;
		return *this;
	}
	inline constexpr value_type operator==(const ModInt& rhs) const {
		return this->x == rhs.x;
	}
	inline constexpr value_type operator!=(const ModInt& rhs) const {
		return !(*this == rhs);
	}
	inline constexpr ModInt operator++(signed unused) {
		ModInt res(*this);
		++(*this);
		return res;
	}
	inline constexpr ModInt& operator++() {
		(*this) += 1;
		return (*this);
	}
	inline constexpr ModInt operator--(signed unused) {
		ModInt res(*this);
		--(*this);
		return res;
	}
	inline constexpr ModInt& operator--() {
		(*this) -= 1;
		return (*this);
	}
	inline constexpr ModInt operator+() const {
		return (*this);
	}
	inline constexpr ModInt operator-() const {
		return (*this).x ? ModInt(mod - (*this).x) : ModInt(0);
	}
	friend constexpr ModInt operator+(const ModInt& lhs, const ModInt& rhs) {return ModInt(lhs) += rhs;}
	friend constexpr ModInt operator-(const ModInt& lhs, const ModInt& rhs) {return ModInt(lhs) -= rhs;}
	friend constexpr ModInt operator*(const ModInt& lhs, const ModInt& rhs) {return ModInt(lhs) *= rhs;}
	friend constexpr ModInt operator/(const ModInt& lhs, const ModInt& rhs) {return ModInt(lhs) /= rhs;}
	explicit constexpr operator value_type() const {return x;}
	friend ostream& operator<<(ostream& lhs, const ModInt& rhs) {
		lhs << rhs.x;
		return lhs;
	}
	friend istream& operator>>(istream& lhs, ModInt& rhs) {
		i64 t;
		lhs >> t;
		rhs = ModInt(t);
		return lhs;
	}
private:
	constexpr value_type extgcd(value_type a, value_type b, value_type& x, value_type& y) const {
		value_type d = a;
		if (b == 0) {
			x = 1;
			y = 0;
		} else {
			d = extgcd(b, a%b, y, x);
			y -= a / b * x;
		}
		return d;
	}
	constexpr value_type mod_(i64 x) {
		x %= mod; if (x < 0) x += mod;
		return static_cast<value_type>(x);
	}
};
}; // modint_n
using modint_n::ModInt;
namespace std {
template<modint_n::value_type N> struct is_integral<ModInt<N>> {
	static constexpr integral_constant<bool, true> value = integral_constant<bool, true>();
};
template<modint_n::value_type N> struct is_arithmetic<ModInt<N>> {
	static constexpr integral_constant<bool, true> value = integral_constant<bool, true>();
};
template<modint_n::value_type N> struct is_scalar<ModInt<N>> {
	static constexpr integral_constant<bool, true> value = integral_constant<bool, true>();
};
template<modint_n::value_type N> struct is_floating_point<ModInt<N>> {
	static constexpr integral_constant<bool, false> value = integral_constant<bool, false>();
};
template<modint_n::value_type N> struct is_signed<ModInt<N>> {
	static constexpr integral_constant<bool, false> value = integral_constant<bool, false>();
};
template<modint_n::value_type N> struct is_unsigned<ModInt<N>> {
	static constexpr integral_constant<bool, true> value = integral_constant<bool, true>();
};
} // namespace std
using modint = ModInt<1000000007>;
//using modint = ModInt<998244353>;

#line 1 "math/ModComb.cpp"
/**
 * @title Mod Combination
 * @brief 前計算$O(N + \log mod)$ で実際に計算するときは$O(1)$
 */
template<class T>
struct ModComb {
	vector<T> fact;
	vector<T> facti;
	ModComb(int n) : fact(n+1), facti(n+1) {
		fact[0] = 1;
		for (int i = 1; i < n + 1; i++) {
			fact[i] = fact[i-1] * i;
		}
		facti[n] = 1 / fact[n];
		for (int i = n-1; i >= 0; i--) {
			facti[i] = facti[i+1] * (i + 1);
		}
	}
	T C(int n, int r) const {
		if(n < 0 || r < 0 || n < r) return 0;
		return fact[n] * facti[r] * facti[n-r];
	}
	T P(int n, int r) const {
		if(n < 0 || r < 0 || n < r) return 0;
		return fact[n] * facti[n-r];
	}
	T H(int n, int r) const {
		if(n < 0 || r < 0) return 0;
		return C(n + r - 1, r);
	}
};
using modcomb = ModComb<modint>;

modint solve(int h, int w) {
  if ((h + w) % 3 != 0) return 0;
  int t = (h+w) / 3:
  h -= t;
  w -= t;
  modcomb m(1e7);
  cout << m.C(h+w, h) << endl;
}

int main(){
  int h, w; cin >> h >> w;
  cout << solve(h, w) << endl;
}

Compiler output:
math/ModComb.cpp: In function 'modint solve(int, int)':
math/ModComb.cpp:36:20: error: expected ',' or ';' before ':' token
math/ModComb.cpp:41:1: warning: control reaches end of non-void function [-Wreturn-type]