11.2 模拟赛

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<algorithm>
 4 #include<cstring>
 5 #include<cstdlib>
 6 #include<cmath>
 7 #include<vector>
 8 #include<queue>
 9 #define inf 2147483611
10 #define ll long long
11 #define MAXN 10101
12 using namespace std;
13 inline int read()
14 {
15     int x=0,f=1;char ch=getchar();
16     while(!isdigit(ch)) {if(ch==‘-‘) f=-1;ch=getchar();}
17     while(isdigit(ch)) {x=x*10+ch-‘0‘;ch=getchar();}
18     return x*f;
19 }
20 int n,m,first[MAXN],next[MAXN*20],to[MAXN*20],cnt;
21 int st[MAXN],top,scc,stp,dfn[MAXN],low[MAXN],now;
22 bool vis[MAXN];
23 int T;
24 void add(int u,int v) {next[++cnt]=first[u],first[u]=cnt,to[cnt]=v;}
25 void tarjan(int x)
26 {
27     low[x]=dfn[x]=++stp,vis[x]=1,st[++top]=x;
28     for(int i=first[x];i;i=next[i])
29     {
30         if(!dfn[to[i]]) {tarjan(to[i]);low[x]=min(low[x],low[to[i]]);}
31         else if(vis[to[i]]) low[x]=min(low[x],dfn[to[i]]);
32     }
33     if(low[x]==dfn[x])
34     {
35         scc++,now=0;
36         while(now!=x)
37             now=st[top--],vis[now]=0;
38     }
39 }
40 int main()
41 {
42     freopen("net.in","r",stdin);
43     freopen("net.out","w",stdout);
44     int a,b;
45     T=read();
46     while(T--)
47     {
48         memset(next,0,sizeof(next));
49         memset(to,0,sizeof(to));
50         memset(first,0,sizeof(first));
51         memset(dfn,0,sizeof(dfn));
52         memset(low,0,sizeof(low));
53         memset(vis,0,sizeof(vis));
54         scc=cnt=stp=top=0;
55         n=read(),m=read();
56         while(m--)
57         {
58             a=read(),b=read();
59             add(a,b);
60         }
61         for(int i=1;i<=n;i++) if(!dfn[i]) tarjan(i);
62         printf("%d\n",scc);
63     }
64 }