URAL1055[Combinations]

水题，分解质因数。

好像必须先打素数表，反正我打了的。

CODE:

/*

PROGRAM: $PROGRAM

AUTHOR: Su Jiao

DATE: 2010-3-27

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

{

      static const int oo=50000;

      int N,M;

      int answer;

      vector<int> prime;

      vector<int> counter;

      void get_prime()

      {

           prime.push_back(2);

           for (int i=3;i<=oo;i++)

           {

               bool can=true;

               for (int j=0;j<prime.size();j++)

                   if (i%prime[j]==0)

                   {

                      can=false;

                      break;

                   }

               if (can) prime.push_back(i);

           }

      }

      void get_counter(int n,int m)

      {

           counter.resize(prime.size(),0);

           for (int i=n;i>=1;i–)

               for (int j=0,k=i;j<prime.size();j++)

                   while (k%prime[j]==0) k/=prime[j],counter[j]++;

           for (int i=m;i>=1;i–)

               for (int j=0,k=i;j<prime.size();j++)

                   while (k%prime[j]==0) k/=prime[j],counter[j]–;

           for (int i=n-m;i>=1;i–)

               for (int j=0,k=i;j<prime.size();j++)

                   while (k%prime[j]==0) k/=prime[j],counter[j]–;

      }

      public:

      Application()

      {

                   cin>>N>>M;

      }

      int run()

      {

          get_prime();

          get_counter(N,M);

          answer=0;

          for (int i=0;i<counter.size();i++)

              if (counter[i]) answer++;

          cout<<answer<<endl;

          return 0;

      }

};

 

int main()

{

    Application app;

    return app.run();

}