hdu 4043

找规律推公式的题目，公式挺简单的，就是(2 * n)!/(n!)*(n!)*4^n不过因为有用到大数，还是用java比较方便

import java.math.BigInteger;
import java.util.Scanner;

public class Main {
public static void work(int n) {
        BigInteger up = BigInteger.ONE;
for (int i = 2; i <= 2 * n; i++) {
            up = up.multiply(BigInteger.valueOf(i));
        }
        BigInteger down = BigInteger.ONE;
for (int i = 1; i <= n; i++) {
            down = down.multiply(BigInteger.valueOf(2 * i));
        }
        down = down.multiply(down);
        BigInteger gcd = down.gcd(up);
        System.out.println(up.divide(gcd) + "/" + down.divide(gcd));
    }

public static void main(String[] args) {
int T;
        Scanner cin = new Scanner(System.in);
        T = cin.nextInt();
while (T-- > 0) {
int n = cin.nextInt();
            work(n);
        }
    }
}

转载于:https://www.cnblogs.com/moonbay/archive/2011/09/21/2183118.html