loj 1034(最小点基）

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=25911

思路：强连通缩点，在新图中找入度为0的点的个数即可。

 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cstdlib>
 #include<cmath>
 #include<climits>
 #include<algorithm>
 #include<stack>
 #include<map>
 #include<set>
 #include<vector>
 #include<queue>
 #include<list>
 using namespace std;
 #define MAXN 11111
 #define inf 1<<30
 #define INF 1LL<<60
 #define FILL(a,b) memset(a,b,sizeof(a))
 typedef long long ll;
 typedef unsigned long long llu;
 typedef pair<int,int>PP;
 template<class T> inline T Get_MIN(const T &a,const T &b){ return a < b ? a : b; }
 template<class T> inline T Get_MAX(const T &a,const T &b){ return a > b ? a : b; }
 template<class T> inline T ABS(const T &a){ return a <  ? -a : a; }

 struct Edge{
     int v,next;
 }edge[MAXN*];

 int n,m,NE;
 int head[MAXN];

 void Insert(int u,int v)
 {
     edge[NE].v=v;
     edge[NE].next=head[u];
     head[u]=NE++;
 }

 int low[MAXN],dfn[MAXN],color[MAXN];
 bool mark[MAXN];
 int scc_count,cnt;
 stack<int>S;
 void Tarjan(int u)
 {
     low[u]=dfn[u]=++cnt;
     mark[u]=true;
     S.push(u);
     for(int i=head[u];i!=-;i=edge[i].next){
         int v=edge[i].v;
         if(dfn[v]==){
             Tarjan(v);
             low[u]=Get_MIN(low[u],low[v]);
         }else if(mark[v]){
             low[u]=Get_MIN(low[u],dfn[v]);
         }
     }
     if(low[u]==dfn[u]){
         scc_count++;
         int v;
         do{
             v=S.top();
             S.pop();
             mark[v]=false;
             color[v]=scc_count;
         }while(u!=v);
     }
 }

 int degree[MAXN];

 int main()
 {
     int _case,u,v,ans,t=;
     scanf("%d",&_case);
     while(_case--){
         scanf("%d%d",&n,&m);
         NE=;
         FILL(head,-);
         FILL(dfn,);
         FILL(mark,false);
         cnt=scc_count=;
         while(m--){
             scanf("%d%d",&u,&v);
             Insert(u,v);
         }
         for(int i=;i<=n;i++)if(dfn[i]==)Tarjan(i);
         FILL(degree,);
         for(int u=;u<=n;u++){
             for(int i=head[u];i!=-;i=edge[i].next){
                 int v=edge[i].v;
                 if(color[u]!=color[v]){
                     degree[color[v]]++;
                 }
             }
         }
         ans=;
         for(int i=;i<=scc_count;i++)if(degree[i]==)ans++;
         printf("Case %d: %d\n",t++,ans);
     }
     return ;
 }