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; }