POJ2506——Tiling

Tiling

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

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 ;
 }