URAL1024[Permutations]

水题，找环，然后，所有环的节点数求最小公倍数。（置换群的术语我不会O(∩_∩)O~）

CODE:

/*

PROGRAM: $PROGRAM

AUTHOR: Su Jiao

DATE: 2010-3-18

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 <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;

      vector<int> P;

      int gcd(int a,int b)

      {

          return b?gcd(b,a%b):a;

      }

      int lmc(int a,int b)

      {

          return a/gcd(a,b)*b;

      }

      public:

      Application()

      {

                    cin>>N;

                    P.resize(N);

                    for (int i=0;i<N;i++)

                    {

                        cin>>P[i];

                        P[i]–;

                    }

      }

      int run()

      {

          vector<bool> visited(N,false);

          int answer=1;

          for (int i=0;i<N;i++)

              if (!visited[i])

              {

                 int j=i;

                 int counter=0;

                 while (!visited[j])

                 {

                       counter++;

                       visited[j]=true;

                       j=P[j];

                 }

                 answer=lmc(answer,counter);

              }

          cout<<answer<<endl;

          return 0;

      }

};

 

int main()

{

    Application app;

    return app.run();

}