POJ 2486 Apple Tree (树形dp 经典题)

#include <cstdio>
#include <cstring>
#include <vector>
#include <algorithm>
using namespace std;
int const MAX = 205;

vector <int> t[MAX];
int dp[MAX][MAX][2], val[MAX];
int n, m;
bool vis[MAX];

void DFS(int u)
{
    vis[u] = true;
    for(int i = 0; i <= m; i++)
        dp[u][i][0] = dp[u][i][1] = val[u];  //从u出发至少可以获得val[u]个
    int len = t[u].size();
    for(int i = 0; i < len; i++)
    {   
        int v = t[u][i];
        if(!vis[v])
        {
            DFS(v);
            for(int j = m; j >= 0; j--)
            {
                for(int k = 0; k <= j; k++)
                {
                    dp[u][j + 2][1] = max(dp[u][j + 2][1], dp[u][k][1] + dp[v][j - k][1]);
                    dp[u][j + 1][0] = max(dp[u][j + 1][0], dp[u][k][1] + dp[v][j - k][0]);
                    dp[u][j + 2][0] = max(dp[u][j + 2][0], dp[u][k][0] + dp[v][j - k][1]);
                }
            }
        }

    }
}

int main()
{
    while(scanf("%d %d", &n, &m) != EOF)
    {
        memset(dp, 0, sizeof(dp));
        memset(vis, false, sizeof(vis));
        for(int i = 1; i <= n; i++)
        {
            scanf("%d", &val[i]);
            t[i].clear();
        }
        for(int i = 1; i < n; i++)
        {
            int u, v;
            scanf("%d %d", &u, &v);
            t[u].push_back(v);
            t[v].push_back(u);
        }
        DFS(1);
        printf("%d\n", dp[1][m][0]);
    }
}

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int const MAX = 205;

int dp[MAX][MAX][2], val[MAX];
int head[MAX], cnt;
int n, m;
struct Edge
{
    int to, next;
}e[MAX * MAX / 2];

void Add(int x, int y)
{
    e[cnt].to = y;
    e[cnt].next = head[x];
    head[x] = cnt++;
}

void DFS(int u, int fa)
{
    for(int i = 0; i <= m; i++)
        dp[u][i][0] = dp[u][i][1] = val[u];  
    for(int i = head[u]; i != -1; i = e[i].next)
    {   
        int v = e[i].to;
        if(v != fa)
        {
            DFS(v, u);
            for(int j = m; j >= 0; j--)
            {
                for(int k = 0; k <= j; k++)
                {
                    dp[u][j + 2][1] = max(dp[u][j + 2][1], dp[u][k][1] + dp[v][j - k][1]);
                    dp[u][j + 1][0] = max(dp[u][j + 1][0], dp[u][k][1] + dp[v][j - k][0]);
                    dp[u][j + 2][0] = max(dp[u][j + 2][0], dp[u][k][0] + dp[v][j - k][1]);
                }
            }
        }
    }
}

int main()
{
    while(scanf("%d %d", &n, &m) != EOF)
    {
        cnt = 0;
        memset(dp, 0, sizeof(dp));
        memset(head, -1, sizeof(head));
        for(int i = 1; i <= n; i++)
            scanf("%d", &val[i]);
        for(int i = 1; i < n; i++)
        {
            int u, v;
            scanf("%d %d", &u, &v);
            Add(u, v);
            Add(v, u);
        }   
        DFS(1, -1);
        printf("%d\n", dp[1][m][0]);
    }
}