HDU 3836 Equivalent Sets

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同：HDU2767点击打开链接
#include<iostream>#include<stack>#include<cstring>using namespace std;const int N=20000+5;const int M=50000+5;stack<int>s;struct node{    int to,next;}G[M];int head[N],cnt;int indegree[N],outdegree[N];int low[N],dfn[N];int paint[N];int vis[N],sta[N];//int num[N];int index,col;inline void Init(){    cnt=0;index=1;col=1;    memset(head,-1,sizeof(head));    memset(indegree,0,sizeof(indegree));    memset(outdegree,0,sizeof(outdegree));    //memset(num,0,sizeof(num));    memset(low,0,sizeof(low));    memset(dfn,0,sizeof(dfn));    memset(paint,0,sizeof(paint));    memset(sta,0,sizeof(sta));    memset(vis,0,sizeof(vis));    while(!s.empty()) s.pop();}inline void add(int a,int b){    G[cnt].to=b;    G[cnt].next=head[a];    head[a]=cnt++;}inline int Min(int a,int b){    if(a<b) return a;    return b;}inline int Max(int a,int b){    if(a>b) return a;    return b;}void Tarjan(int u){    vis[u]=1;sta[u]=1;    low[u]=dfn[u]=index++;    s.push(u);    for(int i=head[u];i+1;i=G[i].next)    {        int to=G[i].to;        if(!vis[to])        {            Tarjan(to);            low[u]=Min(low[u],low[to]);        }        else if(sta[to])        {            low[u]=Min(low[u],dfn[to]);        }    }    if(low[u]==dfn[u])    {        int k=s.top();        while(u!=k)        {            s.pop();            paint[k]=col;            //num[col]++;            sta[k]=0;            k=s.top();        }        s.pop();        paint[u]=col;        sta[u]=0;        //num[col]++;        col++;    }} int main(){    int n,m;    while(cin>>n>>m)    {        if(m==0)         {            cout<<n<<endl;continue;        }        Init();        while(m--)        {            int a,b;            cin>>a>>b;            add(a,b);        }         for(int i=1;i<=n;i++)        {            if(!vis[i])            {                Tarjan(i);            }        }        col--;        if(col==1)         {            cout<<"0"<<endl;continue;        }        for(int i=1;i<=n;i++)        {            for(int j=head[i];j+1;j=G[j].next)            {                int a=i,b=G[j].to;                if(paint[a]!=paint[b])                {                    indegree[paint[b]]++;                    outdegree[paint[a]]++;                }            }        }        int in=0,out=0;        for(int i=1;i<=col;i++)        {            if(!indegree[i]) in++;            if(!outdegree[i]) out++;        }        cout<<Max(in,out)<<endl;    }    return 0;}
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