sgu143 分类： sgu 2015-03-11 22:11 38人阅读 评论(0) 收藏

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树形dp，贪心思想

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#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<ctime>
#include<cmath>
#include<iostream>
#include<algorithm>

const int MAXN = 16005, INF = (1<<30)-1;

int n , ans = -INF;

int w[MAXN] = {0},f[MAXN] = {0};

int head[MAXN] = {0};
int el = 0;

struct edgetype
{
    int v,next;

    void get(int u0,int v0)
    {
        v = v0;
        next = head[u0];
        head[u0] = el;
    }

}mp[MAXN<<1];


void dfs(int u, int fa)
{
    int v;  

    f[u] = w[u];

    for(int i = head[u]; i ; i = mp[i].next)
       if((v = mp[i].v) != fa) dfs(v , u);

    for(int i = head[u]; i ; i = mp[i].next)
      if((v = mp[i].v) != fa)
        if(f[v] > 0) f[u] += f[v];  
}


int main()
{
#ifndef ONLINE_JUDGE
    freopen("sgu143.in","r",stdin);
    freopen("sgu143.out","w",stdout);
#endif

    scanf("%d",&n);

    for(int i = 1; i <= n;i++)
      scanf("%d",&w[i]);
    for(int i = 1; i < n;i++)
    {
        int u,v;
        scanf("%d%d",&u,&v);

        mp[++el].get(u,v);
        mp[++el].get(v,u);
    }

    dfs(1 ,false);

    for(int i = 1; i <= n;i++)
      ans = std::max(ans , f[i]);

    printf("%d\n",ans);

#ifndef ONLINE_JUDGE    
    fclose(stdin);
    fclose(stdout);
#endif  
}

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