大数 卡特兰数

卡特兰数的公式为:?f[n]=f[n-1]*(4*i-2)/(i+1),由于数一大就需要用大数，下面为代码:

#include<iostream>
using namespace std;
const int maxn = 110;
int a[maxn][maxn]; //a[i][j] a[i]表示第几个卡特兰数,a[i][j]表示第i个卡特兰数的第j位
int b[maxn];	//卡特兰数的长度
void ktl()
{
	int i,j,len,carry,tmp;
	a[1][0] = b[1] = 1;
	len = 1;
	for (i = 2; i <= 100; i++)
	{
		for (j = 0; j < len; j++) //乘法
			a[i][j] = a[i - 1][j] * (4 * i - 2);
		carry = 0;
		for (j = 0; j < len; j++)
		{
			tmp = carry + a[i][j];
			a[i][j] = tmp % 10;
			carry = tmp / 10;
		}
		while (carry)
		{
			a[i][len++] = carry % 10;
			carry /= 10;
		}
		for (j = len - 1; j >= 0; j--)
		{
			tmp = carry * 10 + a[i][j];
			a[i][j] = tmp / (i + 1);
			carry = tmp % (i + 1);
		}
		while (!a[i][len - 1])
			len--;
		b[i] = len;
	}
}
int main()
{
	int n;
	ktl();
	while (cin >> n)
	{
		for (int i = b[n] - 1; i >= 0; i--)
			cout << a[n][i];
		cout << "n";
	}
}