113 lines
2.2 KiB
C++
113 lines
2.2 KiB
C++
#include <cstring>
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#include <cstdlib>
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#include <cstdio>
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#include <iostream>
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#include <algorithm>
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#include <cmath>
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#include <stack>
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using namespace std;
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#define MAXN 200010
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#define clr(x,k) memset((x),(k),sizeof(x))
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struct node
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{
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int st,to,next;
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}
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edge[MAXN];
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int n,m,ct,id;
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int head[MAXN],low[MAXN],dfn[MAXN],belong[MAXN],in[MAXN],to[MAXN];
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bool instack[MAXN];
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stack<int>q;
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void add_e(int i,int u,int v)
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{
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edge[i].st=u;
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edge[i].to=v;
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edge[i].next=head[u];
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head[u]=i;
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}
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void tarjan(int i)
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{
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int j;
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dfn[i]=low[i]=++id;
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q.push(i);
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instack[i]=1;
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for(int u=head[i]; ~u; u=edge[u].next)
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{
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j=edge[u].to;
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if(dfn[j]==0)
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{
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tarjan(j);
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if(low[i]>low[j])
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low[i]=low[j];
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}
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else if(instack[j]&&low[i]>low[j])
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low[i]=dfn[j];
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}
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if(dfn[i]==low[i])
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{
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ct++;
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do
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{
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j=q.top();
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q.pop();
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instack[j]=0;
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belong[j]=ct;
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}
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while(i!=j);
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}
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}
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int main()
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{
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int t,i,u,v,sum1,sum2;
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cin>>t;
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while(t--)
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{
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clr(head,-1);
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clr(low,0);
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clr(dfn,0);
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clr(belong,0);
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clr(in,0);
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clr(to,0);
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while(!q.empty())
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q.pop();
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cin>>n>>m;
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for(i=0; i<m; i++)
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{
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cin>>u>>v;
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add_e(i,u,v);
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}
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id=ct=0;
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for(i=1; i<=n; i++)
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{
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if(!dfn[i])
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tarjan(i);
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}
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if(ct==1)
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{
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cout<<0<<endl;
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continue;
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}
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for(i=1; i<=ct; i++)
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{
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in[i]=to[i]=0;
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}
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for(i=0; i<m; i++)
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{
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if(belong[edge[i].st]!=belong[edge[i].to])
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{
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in[belong[edge[i].st]]++;
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to[belong[edge[i].to]]++;
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}
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}
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sum1=sum2=0;
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for(i=1; i<=ct; i++)
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{
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if(in[i]==0)
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sum1++;
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if(to[i]==0)
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sum2++;
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}
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cout<<max(sum1,sum2)<<endl;
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}
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return 0;
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}
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