[USACO5.3]校园网Network of Schools

http://poj.org/problem?id=1236 

https://www.luogu.org/problemnew/show/P2746 

题解：强连通分量

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
#define endl "\n"
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=1000000+10;
const int M=100000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,p,l,r,u,v;
int ans,cnt,flag,temp,sum,top,col;
int a,b,c,sta[N],vis[N],low[N],dfn[N],si[N],co[N],in[N],out[N];
vector<int>G[N];
void Tarjan(int u){
    dfn[u]=low[u]=++sum;
    vis[u]=1;
    sta[++top]=u;
    for(int i=0,j=G[u].size();i<j;i++){
        int v=G[u][i];
        if(!dfn[v]){
            Tarjan(v);
            low[u]=min(low[v],low[u]);
        }else if(vis[v]){
            low[u]=min(dfn[v],low[u]);
        }
    }
    if(dfn[u]==low[u]){
        co[u]=++col;
        ++si[col];
        while(sta[top]!=u){
            ++si[col];
            co[sta[top]]=col;
            vis[sta[top]]=0;
            --top;
        }
        vis[sta[top]]=0;
        --top;
    }

}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    //ios::sync_with_stdio(false);
    //cin.tie(0);
    //cout.tie(0);
    //scanf("%d",&t);
    //while(t--){
    scanf("%d",&n);
    for(int i=1;i<=n;i++){
        while(~scanf("%d",&m)&&m)
            G[i].push_back(m);
    }
    for(int i=1;i<=n;i++)if(!dfn[i])Tarjan(i);
    for(int i=1;i<=n;i++)
        for(int j=0,k=G[i].size();j<k;j++)
            if(co[i]!=co[G[i][j]])
                in[co[G[i][j]]]++,out[co[i]]++;
    for(int i=1;i<=col;i++)cnt+=in[i]==0,ans+=out[i]==0;
    col==1?cout<<1<<endl<<0<<endl:cout<<cnt<<endl<<max(ans,cnt)<<endl;
    //}

#ifdef DEBUG
	printf("Time cost : %lf s\n",(double)clock()/CLOCKS_PER_SEC);
#endif
    //cout << "Hello world!" << endl;
    return 0;
}