最小路径覆盖问题

#include<queue>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
#define N 400
#define M 6050
const int inf = 0x3f3f3f3f;
inline int rd()
{
    int f=1,c=0;char ch=getchar();
    while(ch<‘0‘||ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}
    while(ch>=‘0‘&&ch<=‘9‘){c=10*c+ch-‘0‘;ch=getchar();}
    return f*c;
}
int n,m,hed[N],cur[N],cnt=-1,S,T;
struct EG
{
    int to,nxt;
    int w;
}e[2*M];
void ae(int f,int t,int w)
{
    e[++cnt].to = t;
    e[cnt].nxt = hed[f];
    e[cnt].w = w;
    hed[f] = cnt;
}
int dep[N],fl[N];
int pre[N],fa[N];
bool vis[N];
queue<int>q;
bool bfs()
{
    memset(dep,0x3f,sizeof(dep));
    memcpy(cur,hed,sizeof(cur));
    dep[S] = 0,vis[S] = 1;q.push(S);
    while(!q.empty())
    {
        int u = q.front();
        q.pop();
        for(int j=hed[u];~j;j=e[j].nxt)
        {
            int to = e[j].to;
            if(e[j].w&&dep[to]>dep[u]+1)
            {
                dep[to] = dep[u]+1;
                if(!vis[to])
                {
                    vis[to] = 1;
                    q.push(to);
                }
            }
        }
        vis[u] = 0;
    }
    return dep[T]!=inf;
}
int dfs(int u,int lim)
{
    if(u==T||!lim)return lim;
    int fl=0,f;
    for(int j=cur[u];~j;j=e[j].nxt)
    {
        cur[u] = j;
        int to = e[j].to;
        if(dep[to]==dep[u]+1&&(f=dfs(to,min(lim,e[j].w))))
        {
            fl+=f,lim-=f;
            e[j].w-=f,e[j^1].w+=f;
            if(!lim)break;
        }
    }
    return fl;
}
int dinic()
{
    int ret = 0;
    while(bfs())
        ret+=dfs(S,inf);
    return ret;
}
bool use[N];
int findfa(int u)
{
    for(int j=hed[u<<1|1];~j;j=e[j].nxt)
    {
        int to = e[j].to;
        if(to==T)continue;
        if(!e[j].w)continue;
        return findfa(to>>1);
    }
    return u;
}
void print(int u)
{
    use[u] = 1;
    printf("%d ",u);
    for(int j=hed[u<<1];~j;j=e[j].nxt)
    {
        int to = e[j].to;
        if(to==S)continue;
        if(e[j].w)continue;
        print(to>>1);
        return ;
    }
}
int main()
{
    n = rd(),m =rd();
    S = 0,T = 1;
    memset(hed,-1,sizeof(hed));
    for(int f,t,i=1;i<=m;i++)
    {
        f = rd(),t = rd();
        ae(f<<1,t<<1|1,1);
        ae(t<<1|1,f<<1,0);
    }
    for(int i=1;i<=n;i++)
    {
        ae(S,i<<1,1);
        ae(i<<1,S,0);
        ae(i<<1|1,T,1);
        ae(T,i<<1|1,0);
    }
    int ans = n-dinic();
    for(int i=1;i<=n;i++)
    {
        if(use[i])continue;
        int u = findfa(i);
        print(u);
        puts("");
    }
    printf("%d\n",ans);
    return 0;
}