Luogu P2532 [AHOI2012]树屋阶梯 卡特兰数

#include<cstdio>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cmath>
#include<cctype>
#include<cstdlib>
#include<vector>
#include<map>
#include<set>
#define ll long long
#define R register ll
static char RD[1<<15],*S=RD,*D=RD;
#define getchar() (S==D&&(D=(S=RD)+fread(RD,1,1<<15,stdin),S==D)?EOF:*S++)
const int W=9,B=1E+9,N=1010,L=1000;
using namespace std;
inline int g() {
    R ret=0,fix=1; register char ch; while(!isdigit(ch=getchar())) fix=ch==‘-‘?-1:fix;
    do ret=ret*10+(ch^48); while(isdigit(ch=getchar())); return ret*fix;
}
struct Int {
    int sz; ll dat[2010];
    Int() {sz=0; memset(dat,0,sizeof(dat));}
    inline void init(int vl) {
        sz=0; while(vl) ++sz,dat[sz]=vl%B,vl/=B;
    } inline void print() {
        printf("%lld",dat[sz]); for(R i=sz-1;i;--i) printf("%09d",dat[i]);
    } 
};
Int operator *(Int a,int b) {
    Int c; R lst=a.sz;
    for(R i=1;i<=lst;++i) c.dat[i]=a.dat[i]*b;
    for(R i=1;i<=lst;++i) c.dat[i+1]+=c.dat[i]/B,c.dat[i]%=B;
    while(c.dat[lst+1]) ++lst,c.dat[lst+1]+=c.dat[lst]/B,c.dat[lst]%=B;
    c.sz=lst; return c;
}
Int ans;
int c[N],n;
inline void add(int x,int v) {
    for(R i=2;i*i<=x;++i) while(x%i==0) x/=i,c[i]+=v; 
    if(x!=1) c[x]+=v;
}
signed main() {
#ifdef JACK
    freopen("NOIPAK++.in","r",stdin);
#endif
    n=g(); for(R i=n+2;i<=2*n;++i) add(i,1);
    for(R i=1;i<=n;++i) add(i,-1);
    ans.dat[1]=ans.sz=1; for(R i=1;i<=2*n;++i) while(c[i]) ans=ans*i,--c[i];
    ans.print();
}