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

#include <bits/stdc++.h>
using namespace std;
#define ll long long
#define inf 0x3f3f3f3f
4000

#define pa pair<int,int>
#define N 2010
inline 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
,low
,dfnum=0,bel
,sz
,scc=0,in
,Topo
,num=0,ans=0;
bool mp

,mp1

,inq
;
char S
;
bitset<N>f
;
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;
}