URAL1078[Segments]

看到题目就想到了线段树，不过这却是一道动态规划题。

然后，先将左端点按降序排，然后求右端点的最长上升子序列（当然，也可以右端升序排，左端最长下降子序列，随你便）。

CODE:

/*

PROGRAM: $PROGRAM

AUTHOR: Su Jiao

DATE: 2010-4-10

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;

using std::priority_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;

 

struct Compare

{

       inline

       bool operator ()(const pair<pair<int,int>,int>& a,

                        const pair<pair<int,int>,int>& b)

       {

            if (a.first.first>b.first.first) return true;

            else if (a.first.first<b.first.first) return false;

            else return a.first.second<b.first.second;

       }

};

class Application

{

      int N;

      vector<pair<pair<int,int>,int> > segment;

      public:

      Application()

      {

            cin>>N;

            segment.resize(N);

            for (int i=0;i<N;i++)

            {

                cin>>segment[i].first.first

                   >>segment[i].first.second;

                segment[i].second=i+1;

            }

      }

      int run()

      {

          sort(segment.begin(),segment.end(),Compare());

          static const int NOPRE=-1;

          vector<int> f(N);

          vector<int> pre(N);

          int answer=0;

          for (int i=0;i<N;i++)

          {

              f[i]=1;

              pre[i]=NOPRE;

              for (int j=0;j<i;j++)

                  if (segment[i].first.first<segment[j].first.first

                      &&segment[j].first.second<segment[i].first.second)

                     if (f[j]+1>f[i])

                     {

                        f[i]=f[j]+1;

                        pre[i]=j;

                     }

              if (f[i]>f[answer]) answer=i;

          }

          cout<<f[answer]<<endl;

          stack<int> output;

          int now=answer;

          while (now!=NOPRE)

          {

                output.push(segment[now].second);

                now=pre[now];

          }

          while (!output.empty())

          {

                cout<<output.top();

                output.pop();

                if (output.empty()) cout<<endl;

                else cout<<” “;

          }

          return 0;

      }

};

 

int main()

{

    Application app;

    return app.run();

}