Tele Broadcast

Tele Broadcast

树上背包

SCUACM2022集训前训练-动态规划 - Virtual Judge (vjudge.net)

注意处理叶子结点

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>

using namespace std;
typedef long long ll;

const int N = 3e3 + 10;
const int INF = 1e9;
int n, m;
int a[N];
int f[N][N];//f[u][x]为以u为根的子树中，让x个人看到的最大利润
int tmp[N], sz[N];
struct Edge
{
	int to, val;
};
vector<vector<Edge> > G(N);
void add(int u, int v, int w)
{
	G[u].push_back({v, w});
}

void dfs(int u)
{
	if (G[u].size() == 0)
	{
		sz[u] = 1;
		f[u][1] = a[u];
		return;
	}
	for (int k = 0; k < G[u].size(); k++)
	{
		int v = G[u][k].to, w = G[u][k].val;
		dfs(v);
		for (int i = 0; i <= sz[u]; i++)
			tmp[i] = f[u][i];
		for (int i = sz[u] + 1; i <= sz[u] + sz[v]; i++)
			tmp[i] = -INF;
		for (int i = 0; i <= sz[u]; i++)
			for (int j = 0; j <= sz[v]; j++)
				tmp[i+j] = max(tmp[i+j], f[u][i] + f[v][j] - w);
		for (int i = 0; i <= sz[u] + sz[v]; i++)
			f[u][i] = tmp[i];
		sz[u] += sz[v];
	}
}
int main()
{
	ios::sync_with_stdio(false), cin.tie(0), cout.tie(0);
	cin >> n >> m;
	for (int u = 1; u <= n - m; u++)
	{
		int k;
		cin >> k;
		while(k--)
		{
			int v, w;
			cin >> v >> w;
			add(u, v, w);
		}
	}
	for (int i = n - m + 1; i <= n; i++)
		cin >> a[i];
	
	dfs(1);
	for (int i = sz[1]; i >= 0; i--)
	{
		if (f[1][i] >= 0)
		{
			cout << i << endl;
			break;
		}
	}
	return 0;
}