题目链接：http://uoj.ac/problem/273
$${Ans=frac{prod _{i=1}^{m}i}{w-n+1}}$$
1 #include<iostream> 2 #include<cstdio> 3 #include<algorithm> 4 #include<vector> 5 #include<cstdlib> 6 #include<cmath> 7 #include<cstring> 8 using namespace std; 9 #define maxn 10010 10 #define llg int 11 #define md 998244353 12 #define yyj(a) freopen(a".in","r",stdin),freopen(a".out","w",stdout); 13 llg n,m,ans,x,w; 14 15 inline int getint() 16 { 17 int w=0; 18 char c=getchar(); 19 while((c<'0' || c>'9') && c!='-') c=getchar(); 20 //if (c=='-') q=1, c=getchar(); 21 while (c>='0' && c<='9') w=w*10+c-'0', c=getchar(); 22 return w; 23 } 24 25 int main() 26 { 27 yyj("a"); 28 cin>>n; 29 for (register llg i=1;i<=n;i++) 30 { 31 x=getint(); 32 w+=x; 33 } 34 ans=1; 35 for (register llg i=1;i<=w;i++) if (i+n!=w+1) ans=1LL*ans*i%md; 36 cout<<ans; 37 return 0; 38 }