BZOJ1093 ZJOI2007最大半连通子图（缩点+dp）

发现所谓半连通子图就是缩点后的一条链之后就是个模板题了。注意缩点后的重边。写了1h+真是没什么救了。

#include<iostream>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;
int read()
{
int x=0,f=1;char c=getchar();
while (c<'0'||c>'9') {if (c=='-') f=-1;c=getchar();}
while (c>='0'&&c<='9') x=(x<<1)+(x<<3)+(c^48),c=getchar();
return x*f;
}
#define N 100010
#define M 1000010
int n,m,P,p
,p_new
,dfn
,low
,stk
,set
,size
,f
,s
,degree
,q
,top=0,cnt=0,t=0,ans=0;
bool flag
;
vector<int> a
;
struct data{int to,nxt;
}edge[M],edge_new[M];
void addedge(int x,int y){t++;edge[t].to=y,edge[t].nxt=p[x],p[x]=t;}
void addedge_new(int x,int y){cnt++;edge_new[cnt].to=y,edge_new[cnt].nxt=p_new[x],p_new[x]=cnt;}
void tarjan(int k)
{
dfn[k]=low[k]=++cnt;
stk[++top]=k;flag[k]=1;
for (int i=p[k];i;i=edge[i].nxt)
if (!dfn[edge[i].to]) tarjan(edge[i].to),low[k]=min(low[k],low[edge[i].to]);
else if (flag[edge[i].to]) low[k]=min(low[k],dfn[edge[i].to]);
if (dfn[k]==low[k])
{
t++;
while (stk[top]!=k)
{
size[t]++;
set[stk[top]]=t;
flag[stk[top]]=0;
top--;
}
size[t]++;set[k]=t;flag[k]=0;top--;
}
}
void topsort()
{
int head=0,tail=0;
for (int i=1;i<=n;i++) if (!degree[i]) q[++tail]=i;
while (tail<n)
{
int x=q[++head];
for (int i=p[x];i;i=edge[i].nxt)
{
degree[edge[i].to]--;
if (!degree[edge[i].to]) q[++tail]=edge[i].to;
}
}
}
void inc(int &x,int y){x+=y;if (x>=P) x-=P;}
int main()
{
freopen("bzoj1093.in","r",stdin);
freopen("bzoj1093.out","w",stdout);
n=read(),m=read(),P=read();
for (int i=1;i<=m;i++)
{
int x=read(),y=read();
addedge(x,y);
}
t=0;
for (int i=1;i<=n;i++)
if (!dfn[i]) tarjan(i);
cnt=0;
for (int i=1;i<=n;i++)
for (int j=p[i];j;j=edge[j].nxt)
if (set[i]!=set[edge[j].to]) a[set[i]].push_back(set[edge[j].to]);
n=t;memset(flag,0,sizeof(flag));
for (int i=1;i<=n;i++)
{
int s=a[i].size();
for (int j=0;j<s;j++)
if (!flag[a[i][j]]) addedge_new(i,a[i][j]),flag[a[i][j]]=1,degree[a[i][j]]++;
for (int j=0;j<s;j++)
flag[a[i][j]]=0;
}
memcpy(p,p_new,sizeof(p));
memcpy(edge,edge_new,sizeof(edge));
topsort();
for (int v=n;v>=1;v--)
{
int i=q[v];
s[i]=1;
for (int j=p[i];j;j=edge[j].nxt)
if (f[edge[j].to]>f[i]) f[i]=f[edge[j].to],s[i]=s[edge[j].to];
else if (f[edge[j].to]==f[i]) inc(s[i],s[edge[j].to]);
f[i]+=size[i];
}
for (int i=1;i<=n;i++) ans=max(ans,f[i]);
int tot=0;
for (int i=1;i<=n;i++) if (f[i]==ans) inc(tot,s[i]);
cout<<ans<<endl<<tot;
fclose(stdin);fclose(stdout);
return 0;
}