洛谷 [P2764]最小路径覆盖问题

二分图应用模版

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cstdlib>
#include <queue>
using namespace std;
const int MAXN=400,MAXM=50005;
int head[MAXN],nume,n,m,maxflow,s,t,cur[MAXN],dep[MAXN];
queue<int>q;
struct edge{
	int to,nxt,cap,flow;
}e[MAXM];
void adde(int from,int to,int cap){
	e[++nume].to=to;
	e[nume].cap=cap;
	e[nume].nxt=head[from];
	head[from]=nume;
}
bool bfs(){
	memset(dep,0,sizeof(dep));
	q.push(s);dep[s]=1;
	while(!q.empty()){
		int u=q.front();q.pop();
		for(int i=head[u];i;i=e[i].nxt){
			int v=e[i].to;
			if(!dep[v]&&e[i].flow<e[i].cap){
				dep[v]=dep[u]+1;
				q.push(v);
			}
		}
	}
	return dep[t];
}
int dfs(int u,int flow){
	if(u==t) return flow;
	int tot=0;
	for(int &i=cur[u];i&&tot<flow;i=e[i].nxt){
		int v=e[i].to;
		if(dep[v]==dep[u]+1&&e[i].flow<e[i].cap){
			if(int t=dfs(v,min(flow-tot,e[i].cap-e[i].flow))){
				e[i].flow+=t;
				e[((i-1)^1)+1].flow-=t;
				tot+=t;
			}
		}
	}
	return tot;
}
void dinic(){
	while(bfs()){
		for(int i=s;i<=t;i++) cur[i]=head[i];
		maxflow+=dfs(s,0x3f3f3f3f);
	}
}
bool f[MAXN];
void print(int u){
	printf("%d ",u);
	f[u]=1;
	for(int i=head[u];i;i=e[i].nxt){
		int v=e[i].to;
		if(v&&!f[v-n]&&e[i].flow){
			print(v-n);
			return;
		}
	}
}
int main(){
	cin>>n>>m;
	s=0;t=n*2+1;
	for(int i=1;i<=m;i++){
		int u,v;
		scanf("%d%d",&u,&v);
		adde(u,v+n,1);adde(v+n,u,0);
	}
	for(int i=1;i<=n;i++){
		adde(s,i,1);adde(i,s,0);
		adde(i+n,t,1);adde(t,i+n,0);
	}
	dinic();
	for(int i=1;i<=n;i++){
		if(!f[i]) print(i),printf("\n");
	}
	printf("%d\n",n-maxflow);
}