poj 1548

最小路徑覆蓋 = n - 最大匹配  

能從a走到b,就連一條有向邊

//tpl
//ipqhjjybj_tpl.h
//header.h
#include <cstdio>
#include <cstdlib>
#include <map>
#include <set>
#include <algorithm>
#include <cstring>
#include <iostream>
#include <vector>
#include <string>

#define mp(x,y) make_pair(x,y)
#define pii pair<int,int>
#define pLL pair<long long ,long long>
#define rep(i,j,k) for(int i = j; i < k;i++)
#define repn(i,j,k) for(int i = j; i <= k;i++)

using namespace std;

const int INF = 0x3f3f3f3f;

const int N = 1300;
int g[N][N];
int cx[N],cy[N];
int mark[N];
int nx,ny;

int dfs(int u)  
{  
    rep(v,0,ny) 
    {  
        if(g[u][v]&&!mark[v])//u和v不要搞反了  
        {  
            mark[v]=1;  
            if(cy[v]==-1||dfs(cy[v]))  
            {  
                cx[u]=v;  
                cy[v]=u;  
                return 1;  
            }  
        }  
    }  
    return 0;  
}  
int maxmatch()  
{  
    int res=0;  
    memset(cx,-1,sizeof(cx));  
    memset(cy,-1,sizeof(cy));  
    rep(i,0,nx)
    {  
        if(cx[i]==-1)  
        {  
            memset(mark,0,sizeof(mark));  
            res+=dfs(i);  
        }  
    }  
    return res;  
}  
int x,y;
map<pii,int> M;
vector<pii >pm; 
int getNum(int x,int y){
	if(M.count(mp(x,y))){
		return M[mp(x,y)];
	}
	pm.push_back(mp(x,y));
	return M[mp(x,y)] = pm.size()-1;
}
int main(){
	while(scanf("%d %d",&x,&y)!=EOF){
		if(x==-1 && y == -1) break;
		M.clear() , pm.clear();
		memset(g,0,sizeof(g));
		int n ;
		getNum(x,y);
		while(scanf("%d %d",&x,&y)!=EOF){
			if(x==0 && y==0) break;
			getNum(x,y);
		}
		n = pm.size();
		rep(i,0,n){
<span style="white-space:pre">			</span>rep(j,0,n){
<span style="white-space:pre">				</span>if(i!=j)
<span style="white-space:pre">				</span>if(pm[i].first <=pm[j].first && pm[i].second <= pm[j].second){
<span style="white-space:pre">					</span>g[i][j] = 1;
<span style="white-space:pre">				</span>}
<span style="white-space:pre">			</span>}
<span style="white-space:pre">		</span>}
		nx = ny = n;
		int ans = maxmatch();
		printf("%d\n",n-ans);
	}
	return 0;
}