记录编号	202537	评测结果	AAAAAAAAAA
题目名称	[SYOI 2015] Asm_Def排兵布阵	最终得分	100
用户昵称	Chenyao2333	是否通过	通过
代码语言	C++	运行时间	0.455 s
提交时间	2015-11-01 14:04:48	内存使用	4.10 MiB

#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long LL;
const int kN = 5e5+10;
const int MOD = 998244353;
int fact[kN]; 
int N, num[kN];

int pow(int d, int k) {
	if (!k) return 1;
	int t = pow(d, k/2);
	t = 1ll*t*t%MOD;
	if (k%2) t = 1ll*t*d%MOD;
	return t;
}

int C(int n, int m) {
	if (n < m) return 0;
	return 1ll*fact[n] * pow(fact[n-m], MOD-2)%MOD * pow(fact[m], MOD-2)%MOD;
}

int main () {
	freopen("asm_formation.in", "r", stdin);
	freopen("asm_formation.out", "w", stdout); 
	fact[0] = 1;
	for (int i = 1; i < kN; i++) fact[i] = 1ll*i*fact[i-1] % MOD;
	
	scanf("%d", &N);
	for (int i = 1; i <= N; i++) scanf("%d", &num[i]);
	
	int ans = 1;
	int sum = 0;
	for (int i = 1; i <= N; i++) {
		sum += num[i];
		ans = 1ll*C(sum-1, num[i]-1)*ans % MOD;
	}
	
	printf("%d\n", ans);
	return 0;
}