hdu 6222 Heron and His Triangle

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=6222

解析：规律：a[n] = 4*a[n-1] - a[n-2]
代码：

import java.io.*;import java.math.BigInteger;import java.util.*;public class Main {    public static Scanner s = new Scanner(System.in);    public static void main(String args[]) throws Exception {        int t;        t = s.nextInt();        while(t-- != 0)        {            BigInteger x = s.nextBigInteger();            BigInteger p = new BigInteger("4"), pp = new BigInteger("2"), k = new BigInteger("4");            BigInteger now = p;            while(now.compareTo(x) < 0)            {                now = p.multiply(k).subtract(pp);                pp = p;                p = now;            }            System.out.println(now);        }    }}