71 lines
1.3 KiB
C++
71 lines
1.3 KiB
C++
#include<cstdio>
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#include<vector>
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#include<stack>
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#include<cstring>
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#include<algorithm>
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using namespace std;
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const int maxn=20005;
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int T,n,m,in0[maxn],out0[maxn];
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vector<int> G[maxn];
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int dfn[maxn],lowlink[maxn],sccno[maxn],dfs_cnt,scc_cnt;
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stack<int> S;
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void dfs(int u)
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{
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dfn[u]=lowlink[u]=++dfs_cnt;
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S.push(u);
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for(int i=0;i<G[u].size();i++)
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{
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int v=G[u][i];
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if(!dfn[v])
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{
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dfs(v);
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lowlink[u]=min(lowlink[u],lowlink[v]);
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}
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else if(!sccno[v]) lowlink[u]=min(lowlink[u],dfn[v]);
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}
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if(lowlink[u]==dfn[u])
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{
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scc_cnt++;
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while(true)
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{
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int x=S.top(); S.pop();
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sccno[x]=scc_cnt;
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if(x==u) break;
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}
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}
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}
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int main()
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{
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#ifdef local
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freopen("pro.in","r",stdin);
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#endif
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scanf("%d",&T);
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while(T-->0)
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{
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scanf("%d%d",&n,&m);
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for(int i=1;i<=n;i++) G[i].clear();
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for(int i=0;i<m;i++)
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{
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int u,v; scanf("%d%d",&u,&v);
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G[u].push_back(v);
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}
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dfs_cnt=0; scc_cnt=0;
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memset(sccno,0,sizeof(sccno));
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memset(dfn,0,sizeof(dfn));
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for(int i=1;i<=n;i++) if(!dfn[i]) dfs(i);
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for(int i=1;i<=scc_cnt;i++) in0[i]=out0[i]=1;
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for(int u=1;u<=n;u++)
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for(int i=0;i<G[u].size();i++)
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{
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int v=G[u][i];
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if(sccno[v]!=sccno[u]) in0[sccno[v]]=out0[sccno[u]]=0;
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}
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int a=0,b=0;
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for(int i=1;i<=scc_cnt;i++) a+=in0[i],b+=out0[i];
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int ans=max(a,b);
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if(scc_cnt==1) ans=0;
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printf("%d\n",ans);
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}
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return 0;
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}
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