POJ 1236 Network of Schools

传送门：http://poj.org/problem?id=1236

实现代码：

#include <cstdio>
#include <algorithm>
#include <cstring>
#include <map>
using namespace std;

const int MAXN=10010;
const int MAXM=50010;

struct Edge{
    int to;
    int next;
}edge[MAXM];

int head[MAXN];
int tot;

void addEdge(int u,int v){
    edge[tot].to=v;
    edge[tot].next=head[u];
    head[u]=tot++;
}

void init(){
    memset(head,-1,sizeof(head));
    tot=0;
}

int LOW[MAXN],DFS[MAXN],Stack[MAXN],Num[MAXN],Belong[MAXN];
bool Instack[MAXN];
int Index;
int scc;
int top;

void Targan(int u){
    LOW[u]=DFS[u]=++Index;
    Stack[top++]=u;
    Instack[u]=true;

    int v;
    for(int i=head[u];i!=-1;i=edge[i].next){
        v=edge[i].to;
        if(!DFS[v]){
            Targan(v);
            if(LOW[u]>LOW[v])
                LOW[u]=LOW[v];
        }else if(Instack[v]&&LOW[u]>DFS[v]){
                LOW[u]=DFS[v];
        }
    }

    if(LOW[u]==DFS[u]){
        scc++;

        do{
            v=Stack[--top];
            Instack[v]=false;
            Belong[v]=scc;
            Num[scc]++;
        }while(v!=u);
    }
}

void Solve(int n){
    memset(Instack,false,sizeof(Instack));
    memset(DFS,0,sizeof(DFS));
    memset(Num,0,sizeof(Num));

    Index=scc=top=0;
    for(int i=1;i<=n;i++)
        if(!DFS[i])
        Targan(i);
}

map<int,int>mp[MAXN];
int out[MAXN],in[MAXN];
int main(){
    int n;
    while(scanf("%d",&n)!=EOF){
        init();

        for(int i=1;i<=n;i++){
            int v;
            while(scanf("%d",&v)&&v){
                addEdge(i,v);
                mp[i][v]=1;
            }
        }
        Solve(n);
         if(scc==1){
            printf("1
0
");
            continue;
        }

        for(int i=1;i<=n;i++)
        for(int j=1;j<=n;j++){
            if(mp[i][j]&&Belong[i]!=Belong[j]){
                out[Belong[i]]++;
                in[Belong[j]]++;
            }
        }

        int ans1=0,ans2=0;
        for(int i=1;i<=scc;i++){
            if(in[i]==0) ans1++;
            if(out[i]==0) ans2++;
        }

        printf("%d
%d
",ans1,max(ans1,ans2));


    }
}