POJ 2506 Tiling 递推

http://poj.org/problem?id=2506


Tiling
Time Limit: 1000MS        Memory Limit: 65536K
Total Submissions: 7462        Accepted: 3646

Description
In how many ways can you tile a 2xn rectangle by 2x1 or 2x2 tiles?
Here is a sample tiling of a 2x17 rectangle.

Input
Input is a sequence of lines, each line containing an integer number 0 <= n <= 250.

Output
For each line of input, output one integer number in a separate line giving the number of possible tilings of a 2xn rectangle.

Sample Input

2
8
12
100
200

Sample Output

3
171
2731
845100400152152934331135470251

1071292029505993517027974728227441735014801995855195223534251

import java.math.BigInteger;import java.util.Scanner;public class Main{    public static void main(String[] args){        Scanner cin = new Scanner(System.in);        int n;        while(cin.hasNext())        {        n = cin.nextInt();        if(n==0)        {System.out.println(1);continue;}        else  if(n==1)        {System.out.println(1);continue;}        else   if(n==2)        {System.out.println(3);continue;}                BigInteger a,b,c;        a = BigInteger.valueOf(1);        b = BigInteger.valueOf(3);        for(int i=3;i<=n;i++)        {        c = b.add(a.multiply(BigInteger.valueOf(2)));        a=b;        b=c;        }        System.out.println(b);        }    }}