洛谷 [P2764]最小路径覆盖问题

#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);
}