Submission #28863607

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Source Code Expand

#include<bits/stdc++.h>
#define int long long
#define N 100010
using namespace std;
const int mo=998244353;
inline int read(){
	int x=0,f=1;char c=getchar();
	while(c<48){if(c=='-')f=0;c=getchar();}
	while(c>=48) x=(x<<3)+(x<<1)+(c^48),c=getchar();
	return f?x:-x;
}
int n,k;
int a[N];
int f[N],finv[N],inv[N];
inline int calc2(int n,int m){
	int res=1;
	for(int i=n;i>=n-m+1;i--) res=res*i%mo;
	return res*finv[m]%mo;
}
signed main(){
	f[0]=f[1]=finv[0]=finv[1]=inv[1]=1;
	for(int i=2;i<=1e5;i++){
		f[i]=f[i-1]*i%mo;
		inv[i]=mo-(mo/i)*inv[mo%i]%mo;
		finv[i]=finv[i-1]*inv[i]%mo;
	}
	n=read();k=read();
	int sum=0;
	for(int i=1;i<=n;i++){
		a[i]=read();
		if(i>1) sum+=a[i];
	}
	if(a[1]-sum-k<0){
		cout<<0<<endl;
		return 0;
	}
	int res=calc2(a[1]-sum-1,k-1);
	for(int i=2;i<=n;i++) res=res*calc2(a[i]+k-1,k-1)%mo;
	cout<<res<<endl;
	return 0;
}

Submission Info

Judge Result