hdu 1261 字串数

解题思路：ACM紫书 第十章 P319 有重复元素的全排列

答案： 所有数的和的阶乘 除以 每个数阶乘的乘积

因为给定 （26*12）！ 会爆掉（long long），这里用java 的BigInteger. 

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

public class Main {
	public static BigInteger jc(BigInteger n) {
		if (n.compareTo(new BigInteger("1")) == 0)
			return new BigInteger("1");
		else
			return n.multiply(jc(n.subtract(new BigInteger("1"))));
	}

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		while (sc.hasNext()) {
			int n = sc.nextInt();
			if (n == 0)
				break;
			BigInteger[] numarr = new BigInteger[n];
			BigInteger n1 = new BigInteger("0");
			BigInteger sum = new BigInteger("1");
			for (int i = 0; i < n; i++) {
				numarr[i] = sc.nextBigInteger();
				n1 = n1.add(new BigInteger("" + numarr[i]));
				sum = sum.multiply(new BigInteger("" + jc(numarr[i])));
			}
			System.out.println("" + jc(n1).divide(sum));
		}
	}
}