BZOJ1143: [CTSC2008]祭祀river 网络流_Floyd_最大独立集

Code:

#include<bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin) 
#define maxn 100000  
#define inf 100000 
#define nex 120 
using namespace std;
struct Edge{
    int from,to,cap;
    Edge(int a=0,int b=0,int c=0):from(a),to(b),cap(c){} 
}; 
queue<int>Q; 
vector<Edge>edges; 
vector<int>G[maxn]; 
void add(int u,int v,int c){
    edges.push_back(Edge(u,v,c)); 
    edges.push_back(Edge(v,u,0)); 
    int m=edges.size(); 
    G[u].push_back(m-2); 
    G[v].push_back(m-1); 
}
int S,T,vis[maxn],d[maxn],current[maxn]; 
int BFS(){
    memset(vis,0,sizeof(vis)); 
    vis[S]=1,d[S]=0; Q.push(S);
    while(!Q.empty()){
        int u=Q.front();Q.pop(); 
        for(int sz=G[u].size(),i=0;i<sz;++i){
            Edge r = edges[G[u][i]]; 
            if(!vis[r.to] && r.cap>0) {
                vis[r.to]=1,d[r.to]=d[u]+1; 
                Q.push(r.to); 
            }
        }
    }
    return vis[T]; 
}
int dfs(int x,int cur){
    if(x==T) return cur; 
    int flow=0,f; 
    for(int sz=G[x].size(),i=current[x];i<sz;++i){
        current[x]=i; 
        Edge r = edges[G[x][i]]; 
        if(d[r.to]==d[x]+1&&r.cap>0) {
            if(f=dfs(r.to,min(cur,r.cap)))  {
                flow+=f,cur-=f;   
                edges[G[x][i]].cap-=f,edges[G[x][i]^1].cap+=f; 
            }
        }
        if(cur==0) break; 
    }
    return flow;            
}
int maxflow(){
    int flow=0; 
    while(BFS()){
        memset(current,0,sizeof(current)); 
        flow+=dfs(S,inf); 
    }
    return flow; 
}
int ck[200][200]; 
int main(){
    // setIO("input"); 
    int n,m;  
    scanf("%d%d",&n,&m); 
    for(int i=1,a,b;i<=m;++i) 
        scanf("%d%d",&a,&b),ck[a][b]=1;  
    for(int i=1;i<=n;++i) ck[i][i]=1;
    for(int k=1;k<=n;++k) 
        for(int i=1;i<=n;++i) 
            for(int j=1;j<=n;++j) if(i!=j && ck[i][k]&&ck[k][j]) ck[i][j]=1;   
    for(int i=1;i<=n;++i) 
        for(int j=1;j<=n;++j)  if(i!=j&&ck[i][j]) add(i,j+nex,1);     
    S=0,T=400; 
    for(int i=1;i<=n;++i)  add(S,i,1),add(i+nex,T,1); 
    printf("%d",n-maxflow()); 
    return 0; 
}