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[N],p_new[N],dfn[N],low[N],stk[N],set[N],size[N],f[N],s[N],degree[N],q[N],top=0,cnt=0,t=0,ans=0;
bool flag[N];
vector<int> a[N];
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;
}