[tarjan缩点] 洛谷P2746 [USACO5.3]校园网Network of Schools

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <stack>
using std::stack;

const int N = 233;

struct node{
    int u,v,next;
    node(){}
    node(int _u,int _v,int _next){
        u = _u;
        v = _v;
        next = _next;
    }
}Edge[N*N];

int head[N*N],Count;
int dfn[N],low[N];
//scc_cnt是联通块的个数（缩点后的点的数量
//sccno是缩点后的序号 
int scc_cnt,step,sccno[N];
int n;

void AddEdge(int u,int v){
    Count++;
    Edge[Count] = node(u,v,head[u]);
    head[u] = Count;
}

void init(){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        int x;
        while(scanf("%d",&x) && x!=0){
            AddEdge(i,x);
        }
    }
}

stack<int>S;
void dfs(int x){
    dfn[x] = low[x] = ++step;
    S.push(x);
    for(int i = head[x];i;i=Edge[i].next){
        int v = Edge[i].v;
        if(!dfn[v]){
            dfs(v);
            low[x] = std::min(low[x],low[v]);
        }
        else if(!sccno[v]) low[x] =std::min(low[x],dfn[v]);
    }
    if(low[x] == dfn[x]){
        scc_cnt++;
        while(1){
            int u = S.top();
            S.pop();
            sccno[u] = scc_cnt;
            if(x==u) break;
        }
    }
}

int To[N],Out[N];

int main(){
    init();
    for(int i=1;i<=n;i++){
        if(!dfn[i]) dfs(i);
    }
    for(int i=1;i<=Count;i++){
        if(sccno[Edge[i].u]!=sccno[Edge[i].v]){
            Out[sccno[Edge[i].u]]++;
            To[sccno[Edge[i].v]]++;
        }
    }
    //To入度 Out出度 
    int ask1=0,ask2=0;
    for(int i=1;i<=scc_cnt;i++){
        if( !To[i] ) ask1++;
        if( !Out[i] ) ask2++;
    }
    int End = std::max(ask1,ask2);
    if(scc_cnt==1){
        printf("1\n0\n");
    }
    else{
        printf("%d\n%d\n",ask1,End);
    }
    return 0;
    
}