poj2663

递推，注意f[0] = 1;

View Code

   
     

    
      #include 
    
      <
    
      iostream
    
      >
    
      
#include 
    
      <
    
      cstdio
    
      >
    
      
#include 
    
      <
    
      cstdlib
    
      >
    
      
#include 
    
      <
    
      cstring
    
      >
    
      

    
      using
    
       
    
      namespace
    
       std;


    
      #define
    
       maxn 31
    
      


    
      int
    
       main()
{

    
      //
    
       freopen("t.txt", "r", stdin);
    
      

    
       
    
      int
    
       f[maxn] 
    
      =
    
       {
    
      1
    
      ,
    
      0
    
      ,
    
      3
    
      ,
    
      0
    
      };
 
    
      for
    
       (
    
      int
    
       i 
    
      =
    
       
    
      4
    
      ; i 
    
      <
    
       maxn; i
    
      ++
    
      )
 {
 f[i] 
    
      =
    
       f[i 
    
      -
    
       
    
      2
    
      ] 
    
      *
    
       
    
      3
    
      ;
 
    
      for
    
       (
    
      int
    
       j 
    
      =
    
       
    
      4
    
      ; i 
    
      -
    
       j 
    
      >=
    
       
    
      0
    
      ; j 
    
      +=
    
       
    
      2
    
      )
 f[i] 
    
      +=
    
       f[i 
    
      -
    
       j] 
    
      *
    
       
    
      2
    
      ;
 }
 
    
      int
    
       n;
 
    
      while
    
       (scanf(
    
      "
    
      %d
    
      "
    
      , 
    
      &
    
      n), n 
    
      !=
    
       
    
      -
    
      1
    
      )
 printf(
    
      "
    
      %d\n
    
      "
    
      , f[n]);
 
    
      return
    
       
    
      0
    
      ;
}