[jzoj 5661] 药香沁鼻 解题报告 (DP+dfs序)

#include<algorithm>
#include<cstring>
#include<iostream>
#include<cstdio>
using namespace std;

const int N=5e3+15;
const int M=1e4+15;
int n,p,ans,tot,tim;
int w[N],f[N],v[N],head[N],dp[N][M],id[N],st[N],ed[N];
struct EDGE
{
    int to,nxt;
}edge[N<<1];
inline int read()
{
    char ch=getchar();int s=0,f=1;
    while (ch<‘0‘||ch>‘9‘) {if (ch==‘-‘) f=-1;ch=getchar();}
    while (ch>=‘0‘&&ch<=‘9‘) {s=(s<<3)+(s<<1)+ch-‘0‘;ch=getchar();}
    return s*f;
}
void add(int u,int v)
{
    edge[++tot]=(EDGE){v,head[u]};
    head[u]=tot;
}
void dfs(int x)
{
    st[x]=++tim;id[tim]=x;
    for (int i=head[x];i;i=edge[i].nxt)
        dfs(edge[i].to);
    ed[x]=tim;
}
int main()
{
    freopen("medicine.in","r",stdin);
    freopen("medicine.out","w",stdout);
    n=read();p=read();
    w[1]=read();f[1]=read();v[1]=read();
    for (int i=2;i<=n;i++)
    {
        w[i]=read();f[i]=read();v[i]=read();
        add(f[i],i);
    }
    dfs(1);
    memset(dp,-0x3f,sizeof(dp));
    dp[1][0]=0;
    for (int i=1;i<=tim;i++)
    {
        int x=id[i];
        for (int j=0;j<=p;j++) if (dp[i][j]>=0)
        {
            if (j+w[x]<=p) dp[i+1][j+w[x]]=max(dp[i+1][j+w[x]],dp[i][j]+v[x]);
            dp[ed[x]+1][j]=max(dp[ed[x]+1][j],dp[i][j]);
            ans=max(ans,dp[i][j]);
        }
    }
    for (int i=0;i<=p;i++) ans=max(ans,dp[tim+1][i]);
    printf("%d\n",ans);
    return 0;
}