java高精度数组

　　POJ1205

　　递推公式为a[i] = 3*a[i-1] - a[i-2], a[1] = 1,a[2] = 3 , i 最高为100;

　　搞懂了使用BigInteger开数组。

　　

 import java.util.*;
 import java.math.*;

 public class Main
 {
     public static void main(String[] args)
     {
         Scanner cin = new Scanner(System.in);
         BigInteger a[] = new BigInteger[101];
         a[1] = BigInteger.ONE;
         a[2] = BigInteger.valueOf(3);
         BigInteger Three = BigInteger.valueOf(3);
         for(int i=3; i<=100; i++)
             a[i] = Three.multiply(a[i-1]).subtract(a[i-2]);
         while(cin.hasNext())
         {
             int n = cin.nextInt();
             System.out.println(a[n]);
         }
     }
 }