BZOJ 1093 [ZJOI 2007] 最大半连通子图 （tarjan+树形DP）

题目链接：BZOJ 1093

tarjan缩点，重新建图，再在图上DP
细节：
1.重新建图后有重边，需再开一个数组记录是由谁更新得到
2.顺着边DP比写记忆化搜索方便
3.前后的两个图的边不要搞混

#include<cstdio>#include<cstring>#include<iostream>#include<stack>#include<queue>using namespace std;#define maxn (100000+10)int N,M,idx=0,tot=0,mnum=0;long long mod,ans=0;int head[maxn],dfn[maxn],low[maxn],vis[maxn],belong[maxn],size[maxn],in[maxn];int head2[maxn],dp[maxn],sai[maxn],hehe[maxn];struct node{int v,next;}e[1000000+10];struct edge{int v,next;}e2[1000000+10];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 k=0;void adde(int u,int v){e[k].v=v; e[k].next=head[u]; head[u]=k++;}void adde2(int u,int v){e2[k].v=v; e2[k].next=head2[u]; head2[u]=k++;}stack<int>q;void tarjan(int u){dfn[u]=low[u]=++idx; vis[u]=1; q.push(u);for(int i=head[u];i!=-1;i=e[i].next){int v=e[i].v;if(!dfn[v]){tarjan(v); low[u]=min(low[u],low[v]);}else if(vis[v])low[u]=min(low[u],dfn[v]);}if(dfn[u]==low[u]){tot++; int now=0,cnt=0;while(now!=u){now=q.top(); q.pop(); cnt++;belong[now]=tot; vis[now]=0;}size[tot]=cnt;}}void re_built(){k=0;for(int u=1;u<=N;u++){for(int i=head[u];i!=-1;i=e[i].next){int v=e[i].v;if(belong[v]!=belong[u]){adde2(belong[u],belong[v]); in[belong[v]]++;}}}}queue<int>Q;void find(){for(int i=1;i<=tot;i++){if(!in[i]){Q.push(i);sai[i]=1; dp[i]=size[i];}}while(!Q.empty()){int u=Q.front(); Q.pop();for(int i=head2[u];i!=-1;i=e2[i].next){int v=e2[i].v; in[v]--;if(!in[v])Q.push(v);if(hehe[v]==u)continue; hehe[v]=u;if(dp[v]==dp[u]+size[v])sai[v]=(sai[u]+sai[v])%mod;if(dp[v]< dp[u]+size[v]){dp[v]=dp[u]+size[v]; sai[v] =sai[u];}}}}int main(){memset(head,-1,sizeof(head));memset(head2,-1,sizeof(head2));N=read(); M=read(); cin>>mod;for(int i=1;i<=M;i++){int a=read(),b=read();adde(a,b);}for(int i=1;i<=N;i++)if(!dfn[i])tarjan(i);re_built();find();for(int i=1;i<=tot;i++){if(dp[i]>mnum){mnum=dp[i]; ans=sai[i];}else if(dp[i]==mnum)ans=(ans+sai[i])%mod;}printf("%d\n",mnum);cout<<ans<<endl;return 0;}