hdu 2067 卡特兰数

熟悉卡特兰数的人一眼就能看出这题该怎么做，恶心的是这题最大数据为35，结果在long long范围之内，可是如果用递推公式不当，运算过程中还会溢出。解决的办法是换一个递推公式，或者写成我下面这样

/*
 * hdu2067/linux.c
 * Created on: 2011-7-31
 * Author    : ben
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

void work();
int main() {
#ifndef ONLINE_JUDGE
    freopen("data.in", "r", stdin);
#endif
    work();
    return 0;
}

int gcd(int a, int b) {
    int c;
    if (!a || !b) {
        return a > b ? a : b;
    }
    c = a % b;
    while (c) {
        a = b;
        b = c;
        c = a % b;
    }
    return b;
}

void work() {
    int n, T = 1, i, temp;
    unsigned long long catalan[40] = { 1, 1, 2, 5, 14, 42 };
    for (i = 5; i < 35; i++) {
        temp = gcd(4 * i + 2, i + 2);
        catalan[i + 1] = catalan[i] / ((i + 2) / temp) * ((4 * i + 2) / temp);
    }
    while (scanf("%d", &n) == 1 && n != -1) {
        printf("%d %d %I64u\n", T++, n, catalan[n] * 2);
    }
}