bzoj2208 [Jsoi2010]连通数（tarjan缩点+拓扑排序+bitset传递闭包）

首先用tarjan缩点，重建图，变成DAG,然后拓扑排序+bitset传递闭包。

#include <bits/stdc++.h>using namespace std;#define ll long long#define inf 0x3f3f3f3f#define pa pair<int,int>#define N 2010inline int read(){    int x=0,f=1;char ch=getchar();    while(ch<'0'||ch>'9'){if(ch=='-')f=-1;ch=getchar();}    while(ch>='0'&&ch<='9') x=x*10+ch-'0',ch=getchar();    return x*f;}int n,dfn[N],low[N],dfnum=0,bel[N],sz[N],scc=0,in[N],Topo[N],num=0,ans=0;bool mp[N][N],mp1[N][N],inq[N];char S[N];bitset<N>f[N];stack<int>qq;void tarjan(int x){    dfn[x]=low[x]=++dfnum;qq.push(x);inq[x]=1;    for(int y=1;y<=n;++y){        if(!mp[x][y]) continue;        if(!dfn[y]) tarjan(y),low[x]=min(low[x],low[y]);        else if(inq[y]) low[x]=min(low[x],dfn[y]);    }    if(dfn[x]==low[x]){        ++scc;while(1){            int y=qq.top();qq.pop();inq[y]=0;            bel[y]=scc;sz[scc]++;if(x==y) break;        }    }}void rebuild(){    for(int x=1;x<=n;++x)        for(int y=1;y<=n;++y)            if(mp[x][y]&&bel[x]!=bel[y])                if(!mp1[bel[x]][bel[y]])                    mp1[bel[x]][bel[y]]=1,in[bel[y]]++,f[bel[x]][bel[y]]=1;}void Topology_sort(){    queue<int>q;    for(int i=1;i<=scc;++i) if(!in[i]) q.push(i);    while(!q.empty()){        int x=q.front();q.pop();Topo[++num]=x;        for(int y=1;y<=scc;++y)            if(mp1[x][y])                if(--in[y]==0) q.push(y);    }}int main(){//  freopen("a.in","r",stdin);    n=read();    for(int i=1;i<=n;++i){        scanf("%s",S+1);        for(int j=1;j<=n;++j) mp[i][j]=S[j]-'0';    }    for(int i=1;i<=n;++i) if(!dfn[i]) tarjan(i);    rebuild();    Topology_sort();    for(int i=1;i<=scc;++i) f[i][i]=1;    for(int i=scc;i>=1;--i){        int x=Topo[i];        for(int y=1;y<=scc;++y)            if(mp1[x][y])                f[x]|=f[y];    }    for(int i=1;i<=scc;++i)        for(int j=1;j<=scc;++j)            if(f[i][j]) ans+=sz[i]*sz[j];    printf("%d\n",ans);    return 0;}