hdu2196 (tree dp, dfs planning twice)

src： http://acm.hdu.edu.cn/showproblem.php?pid=2196

Answer: https://blog.csdn.net/shuangde800/article/details/9732825

In dfs2, use the parent node's dp maximum value or the next largest value to plan the value of each state of the child node ! ! ! In other topics, the value of the child node is generally used to plan the value of each state of the parent node~~~ The dp is located in the stack of the parent node or the dp is analyzed in the stack of the child node~~~

ac code:

#include <iostream>
#include<cstdlib>
#include<algorithm>
#include<cmath>
#include<functional>
#include<utility>
#include<string>
#include<string.h>
#include<vector>
#include<iomanip>
#include<stack>
using namespace std;
#define FOR(i,a,b) for(int i=a;i<=b;i++)
const int inf=99999999;

int n,vis[10005],Enum=0,head[10005];
long long dp[10005][2];
struct
{
    int to,v,ne;
}edge[10005];

void init(){memset(vis,0,sizeof(0));Enum=0;memset(head,-1,sizeof(head));}
void add_edge(int a,int b,int v)
{
    edge[Enum].to=b;edge[Enum].v=v;
    edge[Enum].ne=head[a];
    head[a]=Enum++;
}
void dfs1(int u)
{
    dp[u][0]=0;
    for(int i=head[u];i!=-1;i=edge[i].ne){
        int to=edge[i].to;
        int v=edge[i].v;
        dfs1(to);
        dp[u][0]=max(dp[u][0],dp[to][0]+v);
    }
}
void dfs2(int u)
{
    int max1=0,v1=-1,max2=0,v2;
    for(int i=head[u];i!=-1;i=edge[i].ne){
        int to=edge[i].to,v=edge[i].v;
        int tmp=dp[to][0]+v;
        if(tmp>max1){
            max2=max1;v2=v1;max1=tmp;v1=to;
        }else if(tmp==max1||tmp>max2){
            max2=tmp;v2=to;
        }
    }
    if(u!=1){
        int tmp=dp[u][1];
        if(tmp>max1){
            max2=max1;v2=v1;max1=tmp;v1=-1;
        }
        else if(tmp==max1||tmp>max2){max2=tmp;v2=-1;}
    }
    for(int i=head[u];i!=-1;i=edge[i].ne){
        int to=edge[i].to,v=edge[i].v;

        //cerr<<"u is:"<<u<<"  "<<max1<<' '<<max2<<endl;
        //system("pause");//

        if(to==v1){
            dp[to][1]=max2+v;
        }
        else dp[to][1]=max1+v;

        //cerr<<"to:"<<to<<"  "<<dp[to][1]<<endl;//

        dfs2(to);
    }
}

intmain ()
{
    std::ios::sync_with_stdio(false);
    int b,v;
    while(cin>>n){
        init();
        for(int i=2;i<=n;i++){
            cin>>b>>v;
            add_edge(b,i,v);
        }
        dfs1 ( 1 );

//        cout<<endl;
//        FOR(i,1,n)cout<<dp[i][0]<<' '<<dp[i][1]<<endl;//
//        system("pause");

        dfs2(1);
        FOR(i,1,n){
            //cout<<dp[i][0]<<' '<<dp[i][1]<<endl;
            cout<<max(dp[i][0],dp[i][1])<<endl;
        }

    }
    return 0;
}


/*
7
5 10 10 8 20 9 2
2 1 3 1 4 2 5 2 6 3 7 3 0 0
*/