luogu 2812 校园网络 tarjan

Posted 2021-05-07 guangheli

好久没写过图论了，练练手~

code: 

#include <bits/stdc++.h> 
#define N 10005
#define M 5000090 
#define setIO(s) freopen(s".in","r",stdin) 
using namespace std;        
stack<int>S;                                 
int edges,n,cnt,tot;           
int hd[N],to[M],nex[M],dfn[N],low[N],id[N],in[N],out[N],size[N];                   
void add(int u,int v) 
{
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v;   
} 
void tarjan(int x) 
{
    dfn[x]=low[x]=++cnt,S.push(x);  
    for(int i=hd[x];i;i=nex[i]) 
    { 
        int v=to[i]; 
        if(!dfn[v]) tarjan(v), low[x]=min(low[x], low[v]); 
        else if(!id[v]) low[x]=min(low[x], dfn[v]);    
    }    
    if(low[x]==dfn[x]) 
    {
        ++tot;     
        for(;;) 
        {
            int u=S.top(); S.pop();
            id[u]=tot;        
            if(u==x) break;         
        }
    }
}
int main() 
{ 
    int i,j,x;  
    // setIO("input");  
    scanf("%d",&n); 
    for(i=1;i<=n;++i) for(scanf("%d",&x);x!=0;scanf("%d",&x)) add(i,x);     
    for(i=1;i<=n;++i) if(!dfn[i]) tarjan(i);   
    for(i=1;i<=n;++i) 
    {
        for(j=hd[i];j;j=nex[j]) 
            if(id[i]!=id[to[j]]) ++out[id[i]], ++in[id[to[j]]];   
    }       
    int a=0,b=0;     
    for(i=1;i<=tot;++i) a+=in[i]==0, b+=out[i]==0;    
    printf("%d
%d
",a,max(a,b));       
    return 0; 
}