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

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

2

8

12

100

200

3

171

2731

845100400152152934331135470251

1071292029505993517027974728227441735014801995855195223534251

题目大意：给一个2*n的棋盘，用三种方块（2*2,1*2,2*1）将其铺满，为有多少种可能性。
解题思路：显然f(n)=f(n-1)+f(n-2)*2简单递推就可以。。 但是看样例就知道longlong也存不开。用string型来进行大数相加
Code：

 #include<cstdio>

 #include<string>

 #include<iostream>

 using namespace std;

 string a[];

 string Add(string s1,string s2)

 {

     if (s1.length()<s2.length())

         swap(s1,s2);

     int i,j;

     for(i=s1.length()-,j=s2.length()-;i>=;i--,j--)

     {

         s1[i]=s1[i]+(j>=?s2[j]-'':);

         if(s1[i]-''>=)

         {

             s1[i]=(s1[i]-'')%+'';

             if(i) s1[i-]++;

             else s1=''+s1;

         }

     }

     return s1;

 }

 int main()

 {

     int i,n;

     a[]="",a[]="",a[]="";

     for (i=; i<=; i++)

         a[i]=Add(Add(a[i-],a[i-]),a[i-]);

     while (cin>>n)

        cout<<a[n]<<endl;

     return ;

 }