【BZOJ 2438】[中山市选2011]杀人游戏 概率+联通分量

Tarjan缩点以后对于所有入度为一的点ans++最后特判只有一个点，且无出度或者出度的点都可以被其他查出的情况

#include<cstdio>#include<cstring>#include<iostream>#define maxn 300020#include<vector>using namespace std;vector<int>g[maxn];int n,m,head[maxn],sccno[maxn],in[maxn],ans,size[maxn],used[maxn];int tot=1,q[maxn],top,dfn[maxn],low[maxn],cnt,num,inq[maxn],flag[maxn];struct edge{int v,next;}e[maxn];void adde(int a,int b){e[tot].v=b,e[tot].next=head[a];head[a]=tot++;}void dfs(int u){low[u]=dfn[u]=++num,q[++top]=u,inq[u]=1;for(int v,i=head[u];i;i=e[i].next){if(!dfn[v=e[i].v])dfs(v),low[u]=min(low[u],low[v]);else if(inq[v])low[u]=min(low[u],dfn[v]);}if(low[u]==dfn[u]){++cnt;do{inq[q[top]]=0,size[cnt]++;sccno[q[top]]=cnt;}while(q[top--]!=u);}}void rebuild(){for(int i=1;i<=n;i++){for(int v,j=head[i];j;j=e[j].next){if(sccno[i]!=sccno[v=e[j].v]&&!used[sccno[v]]){in[sccno[v]]++,used[sccno[v]]=1;g[sccno[i]].push_back(sccno[v]); }}for(int v,j=head[i];j;j=e[j].next)if(sccno[i]!=sccno[v=e[j].v])used[sccno[v]]=0;}for(int i=1;i<=cnt;i++)if(!in[i])ans++;for(int i=1;i<=cnt;i++){bool ok=true;for(int j=0;j<g[i].size();j++){if(in[g[i][j]]==1){ok=false;break;}}if(in[i]==0&&size[i]==1&&ok){ans--;break;}}}int main(){scanf("%d%d",&n,&m);for(int a,b,i=1;i<=m;i++){scanf("%d%d",&a,&b);adde(a,b);}for(int i=1;i<=n;i++)if(!dfn[i])dfs(i);rebuild();printf("%.6lf",1-ans*1.0/n);return 0;}