Submission #1247924

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Source Code Expand

#include<iostream>
using namespace std;
typedef long long LL;
const LL mod = 1000000007;

LL modp(LL x, LL n, LL md) {
	if (n == 0)return 1;
	LL res = modp(x*x%md, n / 2, md);
	if (n & 1)res = res*x%mod;
	return res;
}

int main() {
	LL w, h;
	cin >> w >> h;
	//(w+h-2)!/(h-1)!(w-1)!
	//a^(p-2)===a^-1

	LL ans = 1;
	for (int i = 1; i <= w + h - 2; i++) {
		ans *= i;
		ans %= mod;
	}

	for (int i = 1; i <= h - 1; i++) {
		ans *= (modp(i, mod - 2, mod) % mod);
		ans %= mod;
	}
	for (int i = 1; i <= w - 1; i++) {
		ans *= (modp(i, mod - 2, mod) % mod);
		ans %= mod;
	}
	cout << ans%mod << endl;
	getchar();
	getchar();
	return 0;
}

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