P2515 [HAOI2010]软件安装

题目就是树上背包，但要先缩点为DAG

 

#include <iostream>
#include <cstring>
#include <vector>
#include <stack>
using namespace std ;
 const int N=503,M=1003;
  //#define int long long
  #define inf 1e9
 int n,m,in[N],w[N],v[N];
 int pool,low[N],dfn[N];
  
 int cl,col[N];
 int W[N],VAL[N];
  int f[N][M];
 vector<int> g[N],graph[N];
 stack<int> st;
  
 void tarjan(int x){
    st.push(x);
    dfn[x]=low[x]=++pool;
    int i,y;
     
    for(i=0;i<g[x].size();i++){
         y=g[x][i];
         if(!dfn[y]) 
         	tarjan(y),low[x]=min(low[x],low[y]);
         else if(!col[y]) 
         	low[x]=min(low[x],dfn[y]);
    }
    if(dfn[x]==low[x]){
        cl++;
        do{
            y=st.top(); st.pop();
            col[y]=cl;
        }while(x!=y);
    }
 }
  
  void dp(int x){
  	for(int i=0;i<=m;i++){
  		if(i>=W[x]) f[x][i]= VAL[x]; 
  		else f[x][i]= -inf;
  	}
  	int j,k;
       for(int i=0,y;i<graph[x].size();i++){
            y=graph[x][i];
            dp(y);
            for(j=m;j>=0;j--)
             for(k=0;k<=j;k++)
              f[x][j]=max(f[x][j],
              f[x][j-k]+f[y][k]);
       }     
  }
 signed main(){
     int i,j,x,y;
      cin>>n>>m;
      for(i=1;i<=n;i++) cin>>w[i];
      for(i=1;i<=n;i++) cin>>v[i];
      for(i=1;i<=n;i++){
      	cin>>y;
      	if(y) g[y].push_back(i);
      }
      
      for(i=1;i<=n;i++) if(!dfn[i]) tarjan(i);
      for(i=1;i<=n;i++) 
      	W[col[i]]+=w[i],VAL[col[i]]+=v[i];
       
      for(i=1;i<=n;i++)
       for(j=0;j<g[i].size();j++){
             x=col[i],y=col[g[i][j]];
             if(x!=y){ 
             	in[y]++; graph[x].push_back(y);
             }
       }
       
       for(i=1;i<=cl;i++) 
       	if(in[i]==0) graph[0].push_back(i);
       dp(0);
       cout<<f[0][m];
 }