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P3033 [USACO11NOV]Cow Steeplechase G

给出

#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std ;
const int N =1e4, M=3e6+2;
 const int inf =1e9;
 
 int b[N],x1[N],x2[N],y1[N],y2[N];
  
 int all=1,hd[N],go[M],w[M],nxt[M];
    
 int S,T,n,m;
 int dis[M],ans=0,now[M];
    
 void add_(int x,int y,int z){
     nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
     w[all]=z;
     swap(x,y);
     nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
     w[all]=0;
 }
  bool bfs(){
     for(int i=0;i<M;i++)dis[i]=inf;
     queue<int> q;
     q.push(S);
     now[S]=hd[S];
     dis[S]=0;
        
     while(q.empty()==0){
         int x=q.front();
         q.pop();
         for(int i=hd[x];i;i=nxt[i]){
             int y=go[i];
             if(w[i]>0&&dis[y]==inf){
                 dis[y]=dis[x]+1;
                 now[y]=hd[y];
                 q.push(y);
                 if(y==T) return 1;
             }
         }
     }
     return 0;
 }
 int dfs(int x,int sum){
     if(x==T) return sum;
     int k,res=0;
        
     for(int i=now[x];i&& sum ;i=nxt[i]){
         now[x]=i;
         int y=go[i];
         if(w[i]>0&&(dis[y]==dis[x]+1)){
             k=dfs(y,min(sum,w[i]));
             if(k==0) dis[y]=inf;
             w[i]-=k;
             w[i^1]+=k;
             res+=k;
             sum-=k;
         }
     }
     return res;
 }
 void dinic(){
    int ans=0;
    while(bfs()) ans+=dfs(S,inf);
    cout<<n-ans<<endl;
 }
 signed main(){
    cin>>n;
    S=0,T=n+1;
    int i,j;
    for(i=1;i<=n;i++){
        cin>>x1[i]>>y1[i]>>x2[i]>>y2[i];
        if(x1[i]==x2[i]) b[i]=1;
        else b[i]=2;
    }
     
    for(i=1;i<=n;i++) if(b[i]==1) add_(S,i,1);
    for(i=1;i<=n;i++) if(b[i]==2) add_(i,T,1);
     
    for(i=1;i<=n;i++)
     for(j=1;j<=n;j++){
        if(i!=j&&b[i]==1&&b[j]==2){
             
        int Y1=y1[i],Y2=y2[i],Y3=y1[j]; if(Y1<Y2) swap(Y1,Y2);
        int X1=x1[j],X2=x2[j],X3=x1[i]; if(X1>X2) swap(X1,X2);
         
        if(Y1>=Y3&&Y2<=Y3&&X1<=X3&&X2>=X3)
            add_(i,j,1);
        }   
      }
       
    dinic();
 }