HDU 1520  Anniversary party

隔层选取，比较基础的树形DP了。

HDU 2196 Computer

我只想说一句这是毛线DP，明明是图论好么。

两次BFS求出权值和最大的一条链，再用两次BFS更新各点最大值。

搜了一下，真的有人用DP做，貌似更快一些。

#include <iostream>
#include <algorithm>
#include <cstdlib>
#include <cstdio>
#include <cstring>
#include <queue>
#include <cmath>
#include <stack>
#include <map>

#pragma comment(linker, "/STACK:1024000000");
#define EPS (1e-8)
#define LL long long
#define ULL unsigned long long int
#define _LL __int64
#define _INF 0x3f3f3f3f
#define Mod 1000000007
#define LM(a,b) (((ULL)(a))<<(b))
#define RM(a,b) (((ULL)(a))>>(b))

using namespace std;

struct N
{
    int u,v,w,next;
}edge[1200000];

int head[10010];

int Top;

void Link(int u,int v,int w)
{
    edge[Top].u = u;
    edge[Top].v = v;
    edge[Top].w = w;
    edge[Top].next = head[u];
    head[u] = Top++;
}

int dis[10010];

bool mark[10010];

struct Q
{
    int w,v;
    bool operator < (const Q &a) const
    {
        return w < a.w;
    }
};

int bfs(int s)
{
    priority_queue<Q> q;

    Q f,t;
    f.w = 0,f.v = s;
    mark[s] = true;

    q.push(f);

    int Max = 0;

    int ep = s;

    while(q.empty() == false)
    {
        f = q.top();
        q.pop();

        if(f.w > Max)
        {
            ep = f.v;
            Max = f.w;
        }
        for(int p = head[f.v];p != -1; p = edge[p].next)
        {
            if(mark[edge[p].v] == false)
            {
                mark[edge[p].v] = true;
                t.v = edge[p].v;
                t.w = f.w + edge[p].w;
                q.push(t);
            }
        }
    }
    return ep;
}

void Cal_Max_Dis(int s)
{
    priority_queue<Q> q;

    Q f,t;

    f.v = s;
    f.w = 0;

    mark[s] = true;

    q.push(f);

    while(q.empty() == false)
    {
        f = q.top();
        q.pop();

        if(dis[f.v] < f.w)
        {
            dis[f.v] = f.w;
        }

        for(int p = head[f.v];p != -1; p = edge[p].next)
        {
            if(mark[edge[p].v] == false)
            {
                mark[edge[p].v] = true;
                t.v = edge[p].v;
                t.w = f.w + edge[p].w;
                q.push(t);
            }
        }
    }

}


int main()
{
    int n;

    int u,v;

    while(scanf("%d",&n) != EOF)
    {
        memset(head,-1,sizeof(int)*(n+2));

        Top = 0;

        for(int i = 2;i <= n ; ++i)
        {
            scanf("%d %d",&u,&v);
            Link(i,u,v);
            Link(u,i,v);
        }

        memset(mark,false,sizeof(bool)*(n+2));
        int e1 = bfs(1);

        memset(mark,false,sizeof(bool)*(n+2));
        int e2 = bfs(e1);

        //cout<<e1<<" "<<e2<<endl;

        memset(dis,0,sizeof(int)*(n+2));

        memset(mark,false,sizeof(bool)*(n+2));
        Cal_Max_Dis(e1);

        memset(mark,false,sizeof(bool)*(n+2));
        Cal_Max_Dis(e2);

        for(int i = 1;i <= n;++i)
        {
            printf("%d\n",dis[i]);
        }

    }

    return 0;
}