POJ 2186

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tarjan判断强连通分量缩点

强连通分量请膜拜大神
http://blog.csdn.net/xinghongduo/article/details/6195337
http://blog.csdn.net/xinghongduo/article/details/6196292

#include<cstdio>#include<cstdlib>#include<iostream>#include<cstring>#include<vector>#define cl(x) memset(x,0,sizeof(x))#define N 10010using namespace std;struct Stack{    int stack[N],top_;    Stack(){top_=0;}    void clear(){top_=0;}    inline void push(int x){stack[++top_]=x;}    inline void pop(){--top_;}    inline int top(){return stack[top_];}}stack;vector<int> G[N];int n,m,dfn[N],low[N],cnt=0,time=0,in[N],out[N],pos=0,ans=0,f[N],C=0,map[N];bool vis[N],is_point[N],flag=1;void get_smaller(){    C++;    int v=stack.top();    while(dfn[v]!=low[v])    {        map[v]=C;        stack.pop();        v=stack.top();    }    map[v]=C;    stack.pop();}void tarjan(int v){    dfn[v]=low[v]=++time;    vis[v]=1;    stack.push(v);    for(int i=0;i<G[v].size();i++)        if(!dfn[G[v][i]])        {            tarjan(G[v][i]);            low[v]=min(low[v],low[G[v][i]]);        }else        if(vis[G[v][i]])            low[v]=min(low[v],dfn[G[v][i]]);    if(dfn[v]==low[v])get_smaller();}int main(){    scanf("%d%d",&n,&m);    for(int i=0;i<m;i++)    {        int x,y;        scanf("%d%d",&x,&y);        G[x].push_back(y);    }    cl(dfn);cl(low);cl(vis);    for(int i=1;i<=n;i++)f[i]=i;    memset(is_point,1,sizeof(is_point));    for(int i=1;i<=n;i++)        if(!vis[i])tarjan(i);    for(int i=1;i<=n;i++)    {        if(out[map[i]])continue;        for(int j=0;j<G[i].size();j++)        {            if(map[i]!=map[G[i][j]]){out[map[i]]=1;break;}        }    }    for(int i=1;i<=C;i++)    {        if(out[i])cnt++;        else pos=i;    }    if(cnt!=C-1){puts("0");return 0;}    else{        for(int i=1;i<=n;i++)if(map[i]==pos)ans++;    }    printf("%d\n",ans);    return 0;}

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