hdu1520

基本的树形dp

#include <cstring>

#include <cstdio>

#include <vector>

using namespace std;



const int MAX_N = (int)(6e3) + 5;



int n;

int weight[MAX_N];

vector <int> edge[MAX_N];

bool vis[MAX_N];

int dp[MAX_N][2];

int root;



void dfs(int father, int u)

{

    for (int i = 0; i < (int)edge[u].size(); i++)

    {

        int v = edge[u][i];

        if (v != father)

            dfs(u, v);

    }

    dp[u][0] = 0;

    dp[u][1] = weight[u];

    for (int i = 0; i < (int)edge[u].size(); i++)

    {

        int v = edge[u][i];

        if (v == father)

            continue;

        dp[u][0] += max(dp[v][0], dp[v][1]);

        dp[u][1] += dp[v][0];

    }

}



void input()

{

    for (int i = 0; i < n; i++)

    {

        scanf("%d", &weight[i]);

        edge[i].clear();

    }

    memset(vis, 0, sizeof(vis));

    int a, b;

    while (scanf("%d%d", &a, &b), a | b)

    {

        a--;

        b--;

        vis[a] = true;

        edge[a].push_back(b);

        edge[b].push_back(a);

    }

    for (int i = 0; i < n; i++)

    {

        if (!vis[i])

        {

            root = i;

            break;

        }

    }

}



int main()

{

    while (scanf("%d", &n) != EOF)

    {

        input();

        dfs(-1, root);

        printf("%d\n", max(dp[root][0], dp[root][1]));

    }

    return 0;

}

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