HDU 2067 小兔的棋盘

题解：卡特兰数的几何意义，所以答案就是卡特兰数的两倍

#include <cstdio>
#include <iostream>
using namespace std;
#define base 10000
#define len 100
void multiply(int a[],int max,int b){
    int i,array=0;
    for(i=max-1;i>=0;i--){
        array+=b*a[i];
        a[i]=array%base;
        array/=base;
    }
}
void divide(int a[],int max,int b){
    int i,div=0;
    for(i=0;i<max;i++){
        div=div*base+a[i];
        a[i]=div/b;
        div%=b;
    }
}
int main(){
    int n,i,a[101][len];
    memset(a[1],0,len*sizeof(int));
    for(i=2,a[1][len-1]=2;i<101;i++){
        memcpy(a[i],a[i-1],len*sizeof(int));
        multiply(a[i],len,4*i-2);
        divide(a[i],len,i+1);
    }
    int t=1;
    while(scanf("%d",&n),n!=-1){
        printf("%d %d ",t++,n);
        for(i=0;i<len&&a[n][i]==0;i++);
        printf("%d",a[n][i++]);
        for(;i<len;i++)printf("%04d",a[n][i]);
        printf("
");
    }return 0;
}