poj 1236 Network of Schools

#include<iostream>#include<cstdio>#include<cstring>#define N 110#define M 5010using namespace std;struct node{    int to,next;}edge[M];int head[N],tot;int dfn[N],low[N],stap[N],belong[N];int in[N],out[N];bool instack[N];int index,bcnt,top;void init(){    tot=0;    memset(head,-1,sizeof(head));    memset(dfn,0,sizeof(dfn));memset(instack,false,sizeof(instack));memset(in,0,sizeof(in));memset(out,0,sizeof(out));    index=top=bcnt=0;}void insert(int u,int v){    edge[tot].to=v;    edge[tot].next=head[u];    head[u]=tot++;}void tarjan(int u){    dfn[u]=low[u]=++index;instack[u]=true;    stap[++top]=u;    bool flag=true;    for(int i=head[u];i!=-1;i=edge[i].next)    {        int v=edge[i].to;        if(!dfn[v])        {            tarjan(v);            low[u]=min(low[u],low[v]);        }        else if(instack[v]&&dfn[v]<low[u])            low[u]=dfn[v];    }    if(low[u]==dfn[u])    {        int x;        bcnt++;        do{            x=stap[top--];instack[x]=false;            belong[x]=bcnt;        }while(x!=u);    }}int main(){    int n;    int i,j;    int to;    while(scanf("%d",&n)!=EOF)    {        init();        for(i=1;i<=n;i++)        {while(scanf("%d",&to)&&to!=0){insert(i,to);}        }        for(i=1;i<=n;i++)        {            if(!dfn[i])                tarjan(i);        }        for(i=1;i<=n;i++){            for(j=head[i];j!=-1;j=edge[j].next)            {                int v=edge[j].to;                if(belong[i]!=belong[v]){                    out[belong[i]]++;in[belong[v]]++;}            }}int ansa=0,ansb=0;for(i=1;i<=bcnt;i++){if(in[i]==0)ansa++;if(out[i]==0)ansb++;}printf("%d\n",ansa);if(bcnt==1)printf("0\n");elseprintf("%d\n",max(ansa,ansb));    }    return 0;}