codeforces553A
作者:互联网
sol:很显然的组合数,就是把当前的ai个塞进前面里去
模数是质数也很行
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#include <bits/stdc++.h> using namespace std; #define int long long typedef int ll; inline ll read() { ll s=0; bool f=0; char ch=' '; while(!isdigit(ch)) {f|=(ch=='-'); ch=getchar();} while(isdigit(ch)) {s=(s<<3)+(s<<1)+(ch^48); ch=getchar();} return (f)?(-s):(s); } #define R(x) x=read() inline void write(ll x) { if(x<0) {putchar('-'); x=-x;} if(x<10) {putchar(x+'0'); return;} write(x/10); putchar((x%10)+'0'); } #define W(x) write(x),putchar(' ') #define Wl(x) write(x),putchar('\n') const int Mod=1000000007,N=10005; int n,a[N],b[N],dp[N],jc[N]; inline int ksm(int x,int y) { int s=1,bas=x; while(y) { if(y&1) s=s*bas%Mod; bas=bas*bas%Mod; y>>=1; } return s; } inline int C(int n,int m) { return jc[n]*ksm(jc[m],Mod-2)%Mod*ksm(jc[n-m],Mod-2)%Mod; } signed main() { // freopen("codeforces.in","r",stdin); int i,j,k; R(n); b[0]=0; for(i=1;i<=n;i++) { R(a[i]); b[i]=b[i-1]+a[i]; } dp[1]=1; jc[0]=jc[1]=1; for(i=2;i<=b[n];i++) jc[i]=jc[i-1]*i%Mod; for(i=2;i<=n;i++) { dp[i]=dp[i-1]*C(b[i]-1,a[i]-1)%Mod; } Wl(dp[n]); return 0; }View Code
标签:ch,int,ll,codeforces553A,isdigit,Mod,jc 来源: https://www.cnblogs.com/gaojunonly1/p/15436925.html