POJ 1548

//题目类型：二分匹配-最小路径覆盖 

//建图：如果后一个垃圾的位置可以通过前一个垃圾的位置可达，则建立一条边 

#include <iostream>

//#include <conio.h>

using namespace std;

#define arraysize 25

typedef struct garbage

{

    int row;

    int col;

}garbage;

garbage garbages[arraysize*arraysize];

int map[arraysize*arraysize][arraysize*arraysize];

bool final[arraysize*arraysize];

int match[arraysize*arraysize];

int ncount;

bool DFS(int p)

{

     int i,j;

     int t;

     for(i=1;i<=ncount;++i)

     {

         if(map[p][i] && !final[i])

         {

             final[i] = true;

             t = match[i];

             match[i] = p;

             if(t== 0 || DFS(t)) return true;

             match[i] = t;

         }                      

     }                        

     return false;   

}

int mat()

{

    int i,j;

    int maxmatch = 0;

    for(i=1;i<=ncount;++i)

    {

        memset(final,0,sizeof(final));

        if(DFS(i)) maxmatch++;

    }    

    return maxmatch;

}

int main()

{

    //freopen("1.txt","r",stdin);

    int i,j;

    int row,col;

    while(cin>>row>>col)

    {

        if(row==-1 && col==-1)

            break;

        memset(map,0,sizeof(map));

        memset(match,0,sizeof(match));

        ncount = 1;

        garbages[ncount].row = row;

        garbages[ncount].col = col;

        while(cin>>row>>col)

        {

            if(row==0 && col==0)

                 break;

            ncount++;

            garbages[ncount].row = row;

            garbages[ncount].col = col;

        }

        for(i=1;i<=ncount;++i)

        {

            for(j=i+1;j<=ncount;++j)

            {

                 if(garbages[j].col>=garbages[i].col)

                    map[i][j] = 1;               

            }

        }

        cout<<(ncount-mat())<<endl;

    }

    //getch();

    return 0;

}