Submission #3413606

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Source Code Expand

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <map>
using namespace std;
typedef long long  ll;
#define rep(i,s,n)for(ll i=s;i<n;i++)
#define repe(i,s,n)for(ll i=s;i<=n;i++)

static const ll s = 1000001;
static const ll MOD = 1e9 + 7;
ll f[s] = {};
ll POW(ll e, ll n) {
	//cout << e << " " << n << endl;
	if (n == 0) return 1;
	if (n == 1) return e;

	ll t = POW(e, n / 2) % MOD;

	if (n & 1)return ((t * t) % MOD)* e % MOD;
	else return t * t % MOD;
}

void fact() {
	f[0] = 1;
	rep(i, 1, s) f[i] = i * f[i - 1] % MOD;
}
ll nCr(ll n, ll r) {
	return ((f[n] * POW(f[r], MOD - 2) % MOD) * POW(f[n - r], MOD - 2) % MOD) % MOD;
}

int main()
{
	fact();
	ll a, b; cin >> a >> b;

	cout << nCr(a + b - 1, b) << endl;

	return 0;
}

Submission Info

Judge Result