URAL1044[Lucky tickets. Easy!]

水水的DP，就如题目说的那样。

CODE:

/*

PROGRAM: $PROGRAM

AUTHOR: Su Jiao

DATE: 2010-3-25

DESCRIPTION:

$DESCRIPTION

*/

#include <iostream>

using std::cin;

using std::cout;

#include <fstream>

using std::ifstream;

using std::ofstream;

#include <sstream>

using std::stringstream;

using std::endl;

#include <vector>

using std::vector;

#include <string>

using std::string;

#include <stack>

using std::stack;

#include <queue>

using std::queue;

#include <set>

using std::set;

#include <map>

using std::map;

using std::pair;

using std::make_pair;

#include <algorithm>

using std::sort;

#include <cassert>

//using std::assert;

 

class Application

{

      int N;

      public:

      Application()

      {

                    cin>>N;

      }

      int run()

      {

          int forward=N/2;

          int backward=N-forward;

          const int MAX=N*9+1;

          vector<vector<int> > f(N+1,vector<int>(MAX,0));

          //f[i][j]表示不超过i位和为j一共有几种可能

          //f[i][j]=sum{f[i-1][k],0<=j-k<=9}

          //边界f[0][0]=1

          //answer=sum{f[forward][i]*f[backward][i]}}

          f[0][0]=1;

          for (int i=1;i<=N;i++)

              for (int j=0;j<MAX;j++)

                  for (int k=0;k<MAX;k++)

                      if (j-k>=0 && j-k<=9)

                         f[i][j]+=f[i-1][k];

          int answer=0;

          for (int i=0;i<MAX;i++)

              answer+=f[forward][i]*f[backward][i];

          cout<<answer<<endl;

          return 0;

      }

};

 

int main()

{

    Application app;

    return app.run();

}