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);         }     } }