hdu 1297 递推

递推式参考：http://www.2cto.com/kf/201302/190324.html

数据较大，需要用大整数来写。

 1 import java.math.*;
 2 import java.util.Scanner;
 3 
 4 public class Main 
 5 {
 6     public static void main( String[] args )
 7     {
 8         Scanner cin = new Scanner(System.in);
 9         BigInteger[] f = new BigInteger[1001];
10         f[0] = new BigInteger("1");
11         f[1] = new BigInteger("1");
12         f[2] = new BigInteger("2");
13         f[3] = new BigInteger("4");
14         for ( int i = 4; i < 1001; i++ )        
15         {
16             f[i] = f[i - 1].add( f[i - 2] ).add( f[i - 4] );
17         }
18         while ( cin.hasNext() )
19         {
20             int n = cin.nextInt();
21             System.out.println(f[n].toString());
22         }
23     }
24 }