题目：http://www.lydsy.com/JudgeOnline/problem.php?id=2427

先用Tarjan算法缩一次强连通分量，然后建树，DP就可以了。

代码：

#include <iostream>
#include <cstring>
#include <algorithm>
#include <stack>
 
using namespace std;
 
#define MAXN 110
#define MAXM 510
 
struct edge {
    int t;
    edge *next;
    edge () {
        next=NULL;
    }
} *head[MAXN];
 
void AddEdge(int s,int t) {
    edge *p=new(edge);
    p->t=t,p->next=head[s];
    head[s]=p;
}
 
int n,m;
int V[MAXN],w[MAXN],d[MAXN];
 
int dfn[MAXN],low[MAXN],Index=0,scc[MAXN];
bool f[MAXN];
stack<int>S;
 
void Tarjan(int v) {
    dfn[v]=low[v]=++Index;
    f[v]=true;
    S.push(v);
    for (edge *p=head[v];p;p=p->next) {
        if (!dfn[p->t]) {
            Tarjan(p->t);
            low[v]=min(low[v],low[p->t]);
        } else if (f[p->t]) low[v]=min(low[v],low[p->t]);
    }
    if (dfn[v]==low[v]) {
        int u;
        do {
            u=S.top();
            S.pop();
            f[u]=false;
            scc[u]=v;
        } while (u!=v);
    }
}
 
int dp[MAXN][MAXM][2];
 
void Dp(int v) {
    int k=0;
    dp[v][V[v]][0]=w[v];
    for (edge *p=head[v];p;p=p->next) {
        Dp(p->t);
        for (int j=0;j<=m;j++) dp[v][j][k^1]=dp[v][j][k];
        for (int i=0;i<=m-V[v];i++) if (dp[p->t][i][1]) {
            for (int j=V[v];j<=m-i;j++) {
                dp[v][j+i][k^1]=max(dp[v][j+i][k^1],dp[v][j][k]+dp[p->t][i][1]);
            }
        }
        k^=1;
    }
    for (int i=0;i<=m;i++) dp[v][i][1]=dp[v][i][k];
}
 
int main() {
    memset(head,0,sizeof(head));
    cin>>n>>m;
    for (int i=0;i++<n;) cin>>V[i];
    for (int i=0;i++<n;) cin>>w[i];
    for (int i=0;i++<n;) {
        cin>>d[i];
        if (d[i])AddEdge(i,d[i]);
    }
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    for (int i=0;i++<n;) if (!dfn[i]) {
        Tarjan(i);
    }
    for (int i=0;i++<n;) if (scc[i]!=i) {
        w[scc[i]]+=w[i],V[scc[i]]+=V[i];
    }
    memset(head,0,sizeof(head));
    for (int i=0;i++<n;) {
        if (scc[i]==i) {
            if (scc[d[i]]==i)AddEdge(0,i);
            else AddEdge(scc[d[i]],i);
        }
    }
    memset(dp,0,sizeof(dp));
    V[0]=w[0]=0;
    Dp(0);
    int ans=0;
    for (int i=0;i<=m;i++) ans=max(dp[0][i][1],ans);
    cout<<ans<<endl;
    return 0;
}