Submission #1001007

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Source Code Expand

#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; ll w; };

#define rep(i, N) for (int i = 0; i < N; i++)
#define pb push_back

ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int c[5010][5010];

ll comb(int N, int K) {
	if (N < 0 || K < 0 || K > N) return 0;
	return c[N][K];
}

ll H(int N, int K) {
	if (K == 0) return !N;
	return comb(N + K - 1, K - 1);
}

int main() {
	rep(i, 5010) {
		c[i][0] = 1;
		for (int j = 1; j <= i; j++)
			c[i][j] = (c[i - 1][j - 1] + c[i - 1][j]) % MOD;
	}
	int N, A, B, C;
	cin >> N >> A >> B >> C;
	if (B % 2) {
		cout << 0 << endl;
		return 0;
	}
	ll ans = 0;
	for (int a = 0; a <= A; a++) {
		int d = A - a;
		for (int c = 0; c * 3 + d <= C; c++) {
			int b = B / 2;
			ll unko = comb(a+b+c+d, a) * comb(b+c+d, b) % MOD * comb(c+d, c) % MOD;
			int k = C - (c * 3 + d);
			unko = unko * H(k, b) % MOD;
			ans = (ans + unko) % MOD;
		}
	}
	cout << ans << endl;
}

Submission Info

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